Use bounded ranges (string_view) for histogram names.

This CL changes the histogram creation APIs to take a durable
string view (i.e., a pointer+size pair referring to memory that
the programmer has annotated that it will not be freed) instead
of just an implicit pointer. The HistogramBase class internally
represents the name's length and the histogram's flags using
16 bits in order to not grow the in-memory size of Histogram
objects. The name of the histogram is subsequently exposed by
HistogramBase as a string_view.

This CL updates consumers of the histogram name's to use a
string_view of the name. This removes many string length
calculations and string copy operations. For histograms
allocated in shared memory, it also avoids potential out-of-
bounds reads if the underlying string data is modified or
corrupted such that it no longer has a trailing NUL char
at the end of the string.

Lastly, this CL updates a number of call-sites where the
histogram names were being copied into short-lived string
objects for use as search keys into various containers to
perform the functionality without making any unnecessary
copies.

Low-Coverage-Reason: TRIVIAL_CHANGE Use of string_view instead of string/char* in some error/logging paths have low coverage.
AX-Relnotes: n/a
Bug: 393394360, 40818143
Change-Id: Iee9ee5ae62335b9e7815f4ae11bde4ff80cfd4a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6231451
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Antonio Rivera <antoniori@google.com>
Commit-Queue: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1422750}

services/tracing/public/cpp/background_tracing/background_tracing_agent_impl.cc

@@ -80,7 +80,7 @@ void BackgroundTracingAgentImpl::OnHistogramChanged(
     const std::string& rule_id,
     base::Histogram::Sample32 histogram_lower_value,
     base::Histogram::Sample32 histogram_upper_value,
-    const char* histogram_name,
+    std::string_view histogram_name,
     uint64_t name_hash,
     base::Histogram::Sample32 actual_value) {
   if (actual_value < histogram_lower_value ||

services/tracing/public/cpp/background_tracing/background_tracing_agent_impl.h

@@ -49,7 +49,7 @@ class COMPONENT_EXPORT(BACKGROUND_TRACING_CPP) BackgroundTracingAgentImpl
   void OnHistogramChanged(const std::string& rule_id,
                           base::Histogram::Sample32 reference_lower_value,
                           base::Histogram::Sample32 reference_upper_value,
-                          const char* histogram_name,
+                          std::string_view histogram_name,
                           uint64_t name_hash,
                           base::Histogram::Sample32 actual_value);
 
@@ -61,7 +61,7 @@ class COMPONENT_EXPORT(BACKGROUND_TRACING_CPP) BackgroundTracingAgentImpl
   base::Time histogram_last_changed_;
   // Tracks histogram names and corresponding registered callbacks.
   std::map<
-      std::string,
+      std::string /*=rule_id*/,
       std::unique_ptr<base::StatisticsRecorder::ScopedHistogramSampleObserver>>
       histogram_callback_map_;
 

services/tracing/public/cpp/perfetto/custom_event_recorder.cc

@@ -177,8 +177,8 @@ void CustomEventRecorder::LogHistogram(base::HistogramBase* histogram) {
   }
   base::Pickle pickle;
   samples->Serialize(&pickle);
-  std::string buckets =
-      base::Base64Encode(std::string(pickle.data_as_char(), pickle.size()));
+  std::string buckets = base::Base64Encode(
+      std::string_view(pickle.data_as_char(), pickle.size()));
   TRACE_EVENT_INSTANT2("benchmark,uma", "UMAHistogramSamples",
                        TRACE_EVENT_SCOPE_PROCESS, "name",
                        histogram->histogram_name(), "buckets", buckets);

services/tracing/public/cpp/perfetto/custom_event_recorder.h

@@ -67,7 +67,7 @@ class COMPONENT_EXPORT(TRACING_CPP) CustomEventRecorder
   // For each of the Histogram that we are tracking, cache the snapshot of their
   // HistogramSamples from before tracing began. So that we can calculate the
   // delta when we go to LogHistograms.
-  std::map<std::string, std::unique_ptr<base::HistogramSamples>>
+  std::map<std::string, std::unique_ptr<base::HistogramSamples>, std::less<>>
       startup_histogram_samples_;
   std::vector<std::string> histograms_;
   base::ActionCallback user_action_callback_ =

services/tracing/public/cpp/perfetto/histogram_samples_data_source.cc

@@ -37,13 +37,13 @@ std::optional<base::HistogramBase::Sample32> MaybeReferenceValue(
 
 struct HistogramSamplesIncrementalState {
   using InternedHistogramName =
-      perfetto::SmallInternedDataTraits::Index<const char*>;
+      perfetto::SmallInternedDataTraits::Index<std::string_view>;
 
   bool was_cleared = true;
   InternedHistogramName histogram_names_;
 
   size_t GetInternedHistogramName(
-      const char* value,
+      std::string_view value,
       HistogramSamplesDataSource::TraceContext::TracePacketHandle& packet) {
     size_t iid;
     if (histogram_names_.LookUpOrInsert(&iid, value)) {
@@ -52,7 +52,7 @@ struct HistogramSamplesIncrementalState {
     auto* interned_data = packet->set_interned_data();
     auto* msg = interned_data->add_histogram_names();
     msg->set_iid(iid);
-    msg->set_name(value);
+    msg->set_name(value.data(), value.size());
     return iid;
   }
 };
@@ -136,7 +136,7 @@ void HistogramSamplesDataSource::OnStop(const StopArgs&) {
 void HistogramSamplesDataSource::OnMetricSample(
     std::optional<base::HistogramBase::Sample32> reference_lower_value,
     std::optional<base::HistogramBase::Sample32> reference_upper_value,
-    const char* histogram_name,
+    std::string_view histogram_name,
     uint64_t name_hash,
     base::HistogramBase::Sample32 sample) {
   if ((reference_lower_value && sample < reference_lower_value) ||
@@ -148,14 +148,14 @@ void HistogramSamplesDataSource::OnMetricSample(
 }
 
 void HistogramSamplesDataSource::OnAnyMetricSample(
-    const char* histogram_name,
+    std::string_view histogram_name,
     uint64_t name_hash,
     base::HistogramBase::Sample32 sample) {
   OnMetricSampleImpl(histogram_name, name_hash, sample, std::nullopt);
 }
 
 void HistogramSamplesDataSource::OnMetricSampleImpl(
-    const char* histogram_name,
+    std::string_view histogram_name,
     uint64_t name_hash,
     base::HistogramBase::Sample32 sample,
     std::optional<uintptr_t> instance) {

services/tracing/public/cpp/perfetto/histogram_samples_data_source.h

@@ -5,6 +5,7 @@
 #ifndef SERVICES_TRACING_PUBLIC_CPP_PERFETTO_HISTOGRAM_SAMPLES_DATA_SOURCE_H_
 #define SERVICES_TRACING_PUBLIC_CPP_PERFETTO_HISTOGRAM_SAMPLES_DATA_SOURCE_H_
 
+#include <string_view>
 #include <vector>
 
 #include "base/component_export.h"
@@ -45,15 +46,15 @@ class COMPONENT_EXPORT(TRACING_CPP) HistogramSamplesDataSource
   void OnMetricSample(
       std::optional<base::HistogramBase::Sample32> reference_lower_value,
       std::optional<base::HistogramBase::Sample32> reference_upper_value,
-      const char* histogram_name,
+      std::string_view histogram_name,
       uint64_t name_hash,
       base::HistogramBase::Sample32 actual_value);
-  static void OnAnyMetricSample(const char* histogram_name,
+  static void OnAnyMetricSample(std::string_view histogram_name,
                                 uint64_t name_hash,
                                 base::HistogramBase::Sample32 sample);
   // `instance` identifies the instance that registered a callback, or nullopt
   // if this is a global callback.
-  static void OnMetricSampleImpl(const char* histogram_name,
+  static void OnMetricSampleImpl(std::string_view histogram_name,
                                  uint64_t name_hash,
                                  base::HistogramBase::Sample32 sample,
                                  std::optional<uintptr_t> instance);