Update documentation of memory-infra to describe updates to heap profiling.

docs/memory-infra/heap_profiler.md

Index: docs/memory-infra/heap_profiler.md
diff --git a/docs/memory-infra/heap_profiler.md b/docs/memory-infra/heap_profiler.md
index 0910b641bf2ab9b2e67b123158964e99f3232f57..35c42007402dd3440d9de739217ba88473100b3f 100644
--- a/docs/memory-infra/heap_profiler.md
+++ b/docs/memory-infra/heap_profiler.md
@@ -38,20 +38,42 @@ integrated with the chrome://tracing ecosystem.
 By default heap profiling collects pseudo allocation traces, which are based
 on trace events. I.e. frames in allocation traces correspond to trace events
 that were active at the time of allocations, and are not real function names.
-However, you can build a special Linux / Android build that will collect
-real C/C++ stack traces.
+It's also possible to use heap profiling with native, symbolized stack traces.

[awong, 2017/06/22 21:43:51]

Add a note that it's for official builds.

[erikchen, 2017/06/22 21:55:56]

Renamed the sections below to distinguish between Chrome/Chromium builds.

+
+#### Native stack traces (macOS/Windows)
+
+1. Navigate to chrome://flags, and set "enable-heap-profiling" to Enabled
+   (native mode).
+
+2. Use the [TraceOnTap][extension-link] extension to grab a trace.
+
+3. Run the following script to symbolize the trace.
+
+        third_party/catapult/tracing/bin/symbolize_trace <trace file>
+
+4. Load the trace file in `chrome://tracing`. Locate a purple ![M][m-purple]
+   dot, and continue from step *3* from the instructions above. Native stack
+   traces will be shown in the _Heap Details_ pane.
+
+[extension-link]: https://cs.chromium.org/chromium/src/third_party/catapult/experimental/trace_on_tap/?q=traceontap+package:%5Echromium$&dr=CSs
+
+#### Native stack traces (Android/Linux)
+
+On Linux / Android, you need to build Chromium with special flags to use native
+heap profiling.
 
  1. Build with the following GN flags:
 
 	Linux
 
-        enable_profiling = true

[DmitrySkiba, 2017/06/22 21:44:32]

Why are you removing this? Without enable_profiling binaries won't have frame
pointers.

[erikchen, 2017/06/22 21:55:55]

See very long discussion on
https://bugs.chromium.org/p/chromium/issues/detail?id=706654.

Unwinding with frame pointers is fundamentally flawed:
https://bugs.chromium.org/p/chromium/issues/detail?id=706654#c6

And it's unnecessary now to obtain stack traces on Desktop, so there's no point
in specifying it.

+        symbol_level = 1

[awong, 2017/06/22 21:43:51]

Move the `symbol_level` change into a note or section that says its needed for
all custom builds.

[erikchen, 2017/06/22 21:55:56]

Add comments for macOS / Windows w.r.t. symbol_level

 
 
 	Android
 
         arm_use_thumb = false
         enable_profiling = true
+        symbol_level = 1
 
  2. Start Chrome with `--enable-heap-profiling=native` switch (notice
  	`=native` part).