[Docs] Add native heap profiling instructions.

components/tracing/docs/heap_profiler.md

 # Heap Profiling with MemoryInfra
 
 As of Chrome 48, MemoryInfra supports heap profiling. The core principle is
 a solution that JustWorks™ on all platforms without patching or rebuilding,
 intergrated with the chrome://tracing ecosystem.
 
 [TOC]
 
 ## How to Use
 
@@ skipping 15 matching lines @@
       ![Cells containing a heap dump][cells-heap-dump]
 
  5. Scroll down all the way to _Heap Details_.
 
  6. Pinpoint the memory bug and live happily ever after.
 
 [memory-infra]:    memory_infra.md
 [m-purple]:        https://storage.googleapis.com/chromium-docs.appspot.com/d7bdf4d16204c293688be2e5a0bcb2bf463dbbc3
 [cells-heap-dump]: https://storage.googleapis.com/chromium-docs.appspot.com/a24d80d6a08da088e2e9c8b2b64daa215be4dacb
 
+### Native stack traces
+
+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.
+
+ 1. Build with the following GN flags:
+
+        Linux
+
+        enable_profiling = true

[Primiano Tucci (use gerrit), 2016/06/30 14:45:47]

Should we suggest also  enable_full_stack_frames_for_profiling ?
The gn doc says that it has major perf implications, not sure how slower does
this make it.
Maybe suggest as optional

+
+
+        Android
+
+        arm_use_thumb = false
+        enable_profiling = true
+
+ 2. Start Chrome with `--enable-heap-profiling=native` switch (notice
+        `=native` part).
+
+        On Android use the command line tool before starting the app:
+
+        build/android/adb_chrome_public_command_line --enable-heap-profiling=native
+
+        (run the tool with an empty argument `''` to clear the command line)
+
+ 3. Grab a [MemoryInfra][memory-infra] trace. You don't need any other
+        categories besides `memory-infra`.
+
+ 4. Save the grabbed trace file. This step is needed because freshly
+        taken trace file contains raw addresses (which look like `pc:dcf5dbf8`)
+        instead of function names, and needs to be symbolized.
+
+ 4. Symbolize the trace file. During symbolization addresses are resolved to
+        the corresponding function names and trace file is rewritten (but a backup
+        is saved with `.BACKUP` extension).
+
+        Linux
+
+        third_party/catapult/tracing/bin/symbolize_trace <trace file>
+
+        Android
+
+        third_party/catapult/tracing/bin/symbolize_trace --output-directory out/Release <trace file>
+
+        (note `--output-directory` and make sure it's right for your setup)

[Primiano Tucci (use gerrit), 2016/06/30 14:45:47]

I think this note is really redundant :)

+
+ 5. 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.
+
 ## Heap Details
 
 The heap details view contains a tree that represents the heap. The size of the
 root node corresponds to the selected allocator cell.
 
 *** aside
 The size value in the heap details view will not match the value in the selected
 analysis view cell exactly. There are three reasons for this. First, the heap
 profiler reports the memory that _the program requested_, whereas the allocator
 reports the memory that it _actually allocated_ plus its own bookkeeping
@@ skipping 59 matching lines @@
 memory allocated by PartitionAlloc alone, the total renderer memory increase was
 around 72 MiB.)
 
 ![Diff of The Verge before and after loading ads][diff]
 
 [pseudo-stack]:            https://storage.googleapis.com/chromium-docs.appspot.com/058e50350836f55724e100d4dbbddf4b9803f550
 [break-down-by-backtrace]: https://storage.googleapis.com/chromium-docs.appspot.com/ec61c5f15705f5bcf3ca83a155ed647a0538bbe1
 [break-down-by-type]:      https://storage.googleapis.com/chromium-docs.appspot.com/2236e61021922c0813908c6745136953fa20a37b
 [type-then-backtrace]:     https://storage.googleapis.com/chromium-docs.appspot.com/c5367dde11476bdbf2d5a1c51674148915573d11
 [diff]:                    https://storage.googleapis.com/chromium-docs.appspot.com/802141906869cd533bb613da5f91bd0b071ceb24