[tracing] Add native allocation tracing mode.

base/trace_event/heap_profiler_allocation_context.h

Index: base/trace_event/heap_profiler_allocation_context.h
diff --git a/base/trace_event/heap_profiler_allocation_context.h b/base/trace_event/heap_profiler_allocation_context.h
index 8544c78eb2cd34c3f7693fa4063ccdcf85f837a1..48670680b7083e28b74ec54483e84643033150c8 100644
--- a/base/trace_event/heap_profiler_allocation_context.h
+++ b/base/trace_event/heap_profiler_allocation_context.h
@@ -35,9 +35,15 @@ namespace trace_event {
 //
 // See the design doc (https://goo.gl/4s7v7b) for more details.
 
-using StackFrame = const char*;
+using StackFrame = const void*;
+
+enum StackFrameType {

[Primiano Tucci (use gerrit), 2016/04/01 15:56:28]

do we really need this run-time information per each frame?
In other words, do we ever want to support the case where some stack frames are
native and others are pseudo?
Or should that be just a global setting?

[Dmitry Skiba, 2016/04/04 22:38:33]

It's called that way, but it's used per backtrace, not per frame. I think that
we should go another direction - introduce it per-frame, so that we could for
example add things like thread names to native stack traces. And other way
around too - Sid has an idea to add addresses of task functions to pseudo stack
traces. Those addresses always available, and provide precise place where
task-related allocations stem from.

+  STACK_FRAME_TYPE_SYMBOL,  // const char* string
+  STACK_FRAME_TYPE_PC       // as returned by StackTrace::Addresses()
+};
 
 struct BASE_EXPORT Backtrace {
+  StackFrameType frame_type;
   // Unused backtrace frames are filled with nullptr frames. If the stack is
   // higher than what can be stored here, the bottom frames are stored. Based
   // on the data above, a depth of 12 captures the full stack in the vast