[tracing] Add thread name to the pseudo stack of heap profiler

base/trace_event/heap_profiler_allocation_context_tracker.cc

Index: base/trace_event/heap_profiler_allocation_context_tracker.cc
diff --git a/base/trace_event/heap_profiler_allocation_context_tracker.cc b/base/trace_event/heap_profiler_allocation_context_tracker.cc
index 2877d2af91b27ace28839ebaac7468322cf4823f..19fa8ac313de4788794c4d914ce0a5f6cbeef023 100644
--- a/base/trace_event/heap_profiler_allocation_context_tracker.cc
+++ b/base/trace_event/heap_profiler_allocation_context_tracker.cc
@@ -49,12 +49,19 @@ AllocationContextTracker::GetInstanceForCurrentThread() {
   return tracker;
 }
 
-AllocationContextTracker::AllocationContextTracker() {
+AllocationContextTracker::AllocationContextTracker() : thread_name_(nullptr) {
   pseudo_stack_.reserve(kMaxStackDepth);
 }
 AllocationContextTracker::~AllocationContextTracker() {}
 
 // static
+void AllocationContextTracker::SetCurrentThreadName(const char* name) {

[Primiano Tucci (use gerrit), 2016/03/25 02:14:30]

after me cl lands this should be just sa call to te method instance

[ssid, 2016/03/25 05:57:09]

Yes i did not want this to be a member because i would have to move this check
outside. so at thread id manager i will write,
if capture_enabled then get instance and set name.
More code in threadIdManager and it need not be there. Also, if i have to move
this part into Platformthread if base owners didn't agree then i will have to
copy this if condition to 5 places. So, better to have the if here.

If I do not check for capture_enabled before getting the instance, then i will
end up creating the tracker even if heap profiling is not enabled, causing all
the allocations(comes out ~1Kib per thread).

[Primiano Tucci (use gerrit), 2016/03/25 15:27:55]

Ahh ok makes sense. Although our code style [1] seems to state "For iterators
and other template types, use pre-increment", So I think you want to split that
into two lines. 

[1]
https://google.github.io/styleguide/cppguide.html#Preincrement_and_Predecrement

+  if (name && capture_enabled()) {
+    GetInstanceForCurrentThread()->thread_name_ = name;
+  }
+}
+
+// static
 void AllocationContextTracker::SetCaptureEnabled(bool enabled) {
   // When enabling capturing, also initialize the TLS slot. This does not create
   // a TLS instance yet.
@@ -103,6 +110,10 @@ AllocationContext AllocationContextTracker::GetContextSnapshot() {
     auto src_end = pseudo_stack_.end();
     auto dst_end = std::end(ctx.backtrace.frames);
 
+    // Add the thread name as the first enrty in the backtrace.
+    if (thread_name_)
+      *src++ = thread_name_;

[Primiano Tucci (use gerrit), 2016/03/25 02:14:31]

are you not clobbering the first valid stack entry by doing this?

[ssid, 2016/03/25 05:57:09]

Sorry I meant dst++ here!

[Primiano Tucci (use gerrit), 2016/03/25 15:27:55]

Ah right, that makes more sense :)

+
     // Copy as much of the bottom of the pseudo stack into the backtrace as
     // possible.
     for (; src != src_end && dst != dst_end; src++, dst++)