[UMA] Add performance profile data to UMA uploads.

base/tracked_objects.cc

Index: base/tracked_objects.cc
diff --git a/base/tracked_objects.cc b/base/tracked_objects.cc
index 38b9320eb5a653d6db254633f7483bd6d8d9c00a..2c845001b754cf3417246b0414dc37363e25b74f 100644
--- a/base/tracked_objects.cc
+++ b/base/tracked_objects.cc
@@ -648,21 +648,9 @@ void ThreadData::Reset() {
 }
 
 static void OptionallyInitializeAlternateTimer() {
-  char* alternate_selector = getenv(kAlternateProfilerTime);
-  if (!alternate_selector)
-    return;
-  switch (*alternate_selector) {
-    case '0':  // This is the default value, and uses the wall clock time.
-      break;
-    case '1':  {
-      // Use the TCMalloc allocations-on-thread as a pseudo-time.
-      ThreadData::SetAlternateTimeSource(GetAlternateTimeSource());
-      break;
-      }
-    default:
-      NOTREACHED();
-      break;
-  }
+  NowFunction* alternate_time_source = GetAlternateTimeSource();
+  if (alternate_time_source)
+    ThreadData::SetAlternateTimeSource(alternate_time_source);

[jar (doing other things), 2012/04/20 02:10:10]

This is an interesting change.  Is the justification that we we check for the
environment variable in the allocator shim for TCMalloc, and that suffices?

If I had to delete such partially repetitious code from any one place, it would
probably be from the TCMalloc setter.  This code is more general, and is
probably the hub location to both decide, and to (some day) record the decision
that was made so that it can be used for filling protobufs and such.

Am I missing something?

[Ilya Sherman, 2012/04/20 22:26:21]

Yep, that seems to be how the code was already set up.  Note that the previously
existing code called into GetAlternateTimeSource(), just as the new code does --
the allocator shim seems to be responsible for actually setting the alternate
time source to be based on TCMalloc.  My guess is that this is because TCMalloc
lives in third_part/, and base/ typically shouldn't have dependencies on
third_party/.  It looks like base/allocator/ has a whole gyp file dedicated to
setting up a special-case exception.

You probably know better than I do: is it ok to #include
third_party/tcmalloc/chromium/src/thread_cache.h in the tracked_objects file? 
That seems to be where the alternate time source --
GetBytesAllocatedOnCurrentThread() -- is declared.
Right now it looks like base/profiler/alternate_timer.{h, cc} is keeping track
of the bookkeeping for that.  Does that sound ok to you, or would you strongly
prefer to have the logic live within the tracked_objects.cc implementation file?

 }
 
 bool ThreadData::Initialize() {