Update documentation for heap profiler.

Change-Id: Icf63c40bfeb356bb219a9ba0f8fd215030bc45f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531229
Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642244}

docs/memory-infra/heap_profiler.md

@@ -4,41 +4,29 @@ As of Chrome 48, MemoryInfra supports heap profiling. Chrome will track all live
 allocations (calls to new or malloc without a subsequent call to delete or free)
 along with sufficient metadata to identify the code that made the allocation.
 
+By default, MemoryInfra traces will not contain heap dumps. Heap profiling must
+be enabled via chrome://memory-internals or about://flags.
+
 [TOC]
 
 ## How to obtain a heap dump (M66+, Linux, macOS, Windows)
 
- 1. Navigate to chrome://flags and search for `memlog`.
+ 1. Navigate to chrome://memory-internals.
-
+    * There will be an error message at the top if heap-profiling is not
- 2. Choose the process types you want to profile with the `memlog` flag. The
+      supported on the current configuration
-    most common setting is `Only Browser`.
+ 2. Enable heap profiling for the relevant processes. Future allocations will be
-
+    tracked. Refresh the page to view tracked processes.
- 3. You can control resolution of sampling with `memlog-sampling-rate`.
+    * To enable tracking at process start, navigate to chrome://flags and search
-    By default samples are collected with the average interval of 100KB.
+      for `memlog`.
-    On versions prior Chrome 75 you can enable `memlog-keep-small-allocations`
+ 3. To take a heap dump, click `save dump`. This is stored as a
-    to record all the allocations, however this option has a significant
+    [MemoryInfra][memory-infra] trace.
-    performance and memory overhead.
+ 4. To symbolize the trace:
-
- 4. By default, stack traces use native stack traces, which does not contain any
-    thread information. To include the thread at time of allocation, set
-    `memlog-stack-mode` to `native with thread names`.
-
- 5. Restart Chrome.
-
- 6. Grab a [MemoryInfra][memory-infra] trace.
-
- 7. Save the trace.
-
- 8. To symbolize the trace:
    * Windows only: build `addr2line-pdb` from the chromium repository. For subsequent commands, add the flag `--addr2line-executable=<path_to_addr2lin-pdb>`
    * If this is a local build, run the command `./third_party/catapult/tracing/bin/symbolize_trace --is-local-build <path_to_trace>`
    * If this is an official Chrome build,  run `./third_party/catapult/tracing/bin/symbolize_trace <path_to_trace>`. This will request authentication with google cloud storage to obtain symbol files [googlers only].
    * If this is an official macOS or Linux Chrome build, add the flag `--use-breakpad-symbols`.
    * If the trace is from a different device, add the flag `--only-symbolize-chrome-symbols`.
-
+ 5. Load the (now symbolized) trace in chrome://tracing.
- 9. Turn off heap profiling in chrome://flags. Restart Chrome.
-
- 10. Load the (now symbolized) trace in chrome://tracing.
 
 ## How to obtain a heap dump (M66+, Android)