Adding instrumentation to locate the source of jankiness.

Mechanical change that adds instrumentation required to locate the source of
jankiness (i.e. a long-running fragment of code executed as a part of the task
that causes jank) in the code. See the bug for details on what kind of jank we
are after.  A number of similar CLs were landed, and none of them caused issues.
The code of the instrumentation is highly optimized and is not expected to
affect performance. The code simply creates a diagnostic task which is identical
to ones created by PostTask or IPC message handlers.

BUG=455884,455942,455952
TEST=none
TBR=mmenke,michaeln,zea

Review URL: https://codereview.chromium.org/900793009

Cr-Commit-Position: refs/heads/master@{#314970}

1 files changed, 6 insertions, 0 deletions

diff --git a/content/browser/loader/resource_dispatcher_host_impl.cc b/content/browser/loader/resource_dispatcher_host_impl.cc
index fa9c044..f8264c2 100644
--- a/content/browser/loader/resource_dispatcher_host_impl.cc
+++ b/content/browser/loader/resource_dispatcher_host_impl.cc
@@ -21,6 +21,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/stl_util.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "content/browser/appcache/appcache_interceptor.h"
@@ -2151,6 +2152,11 @@ void LoadInfoUpdateCallback(const LoadInfoMap& info_map) {
 }  // namespace
 
 void ResourceDispatcherHostImpl::UpdateLoadStates() {
+  // TODO(pkasting): Remove ScopedTracker below once crbug.com/455952 is
+  // fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "455952 ResourceDispatcherHostImpl::UpdateLoadStates"));
   // Populate this map with load state changes, and then send them on to the UI
   // thread where they can be passed along to the respective RVHs.
   LoadInfoMap info_map;