[shared storage] Add AbsoluteUsefulResourceDuration UMA

Why: This helps to see if there are long-running worklets, which can
impact performance or be exploited for side-channel attacks. If the
result reveals such instances, we will further add UKM to investigate
the specific use cases.

Given that the existing 'UsefulResourceDuration' represents a
percentage, we add 'AbsoluteUsefulResourceDuration' for a distinction.

Bug: 398173023
Change-Id: I8b69362158a35b0861033f8f58a0aa335edb4241
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6287655
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1423455}

content/browser/shared_storage/shared_storage_worklet_host.cc

@@ -489,6 +489,24 @@ SharedStorageWorkletHost::~SharedStorageWorkletHost() {
             elapsed_time_since_creation);
   }
 
+  // Initialize to zero. This represents the scenario where the worklet didn't
+  // execute any operations due to early validation failure, ensuring
+  // consistency with the scope of the `UsefulResourceDuration` metric.
+  base::TimeDelta useful_resource_duration;
+  if (pending_operations_count_ > 0) {
+    // Worklet is still processing, so the useful duration is its total
+    // lifetime.
+    useful_resource_duration = elapsed_time_since_creation;
+  } else if (!last_operation_finished_time_.is_null()) {
+    // Worklet finished at least one operation. Useful duration is until the
+    // last operation.
+    useful_resource_duration = last_operation_finished_time_ - creation_time_;
+  }
+
+  base::UmaHistogramTimes(
+      "Storage.SharedStorage.Worklet.Timing.AbsoluteUsefulResourceDuration",
+      useful_resource_duration);
+
   if (!page_) {
     return;
   }

tools/metrics/histograms/metadata/storage/histograms.xml

@@ -1973,6 +1973,20 @@ chromium-metrics-reviews@google.com.
   </summary>
 </histogram>
 
+<histogram
+    name="Storage.SharedStorage.Worklet.Timing.AbsoluteUsefulResourceDuration"
+    units="ms" expires_after="2025-08-21">
+  <owner>cammie@chromium.org</owner>
+  <owner>yaoxia@chromium.org</owner>
+  <owner>chrome-ads-histograms@google.com</owner>
+  <summary>
+    Measures the total duration that a Shared Storage worklet is actively
+    processing operations (i.e, from the worklet's creation until either its
+    last operation completes or it is destroyed). Recorded when the worklet is
+    destroyed.
+  </summary>
+</histogram>
+
 <histogram name="Storage.SharedStorage.Worklet.Timing.Append" units="ms"
     expires_after="2025-08-10">
   <owner>cammie@chromium.org</owner>
@@ -2126,11 +2140,10 @@ chromium-metrics-reviews@google.com.
   <owner>yaoxia@chromium.org</owner>
   <owner>chrome-ads-histograms@google.com</owner>
   <summary>
-    Measures the percentage of the time duration between a
-    `SharedStorageWorkletHost`'s creation and destruction that occurs before the
-    time of its last finished operation. For worklets that are destroyed before
-    completing their outstanding operations, we record 100. Recorded in the
-    destructor of `SharedStorageWorkletHost`.
+    Measures the percentage of a shared storage worklet's lifetime that it is
+    actively processing operations (i.e., from the worklet's creation until
+    either its last operation completes or it is destroyed). If the worklet has
+    zero lifetime, we record 100. Recorded when the worklet is destroyed.
   </summary>
 </histogram>