Adding instrumentation to locate the source of jankiness.

Please see the bug for the context.
Prior instrumentations showed:

The jank happens in more than 1 place:

URLRequest::Delegate::OnResponseStarted   34.3 jph
NetworkDelegate::OnRawBytesRead    16.4 jph
URLRequest::Delegate::OnReadCompleted   7.62 jph
... (the list continues, but further jankiness numbers are quite low)

I need to instrument
the code inside it to find out which part causes jank.

This is a 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. They've
helped to find and fix janky code. 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. The task gets created only in developer build and in Canary channel.

BUG=423948
TBR=jianli,danakj,jhawkins

Review URL: https://codereview.chromium.org/732633002

Cr-Commit-Position: refs/heads/master@{#304653}

1 files changed, 11 insertions, 0 deletions

diff --git a/content/browser/service_worker/service_worker_cache.cc b/content/browser/service_worker/service_worker_cache.cc
index e2796e4..5283a08 100644
--- a/content/browser/service_worker/service_worker_cache.cc
+++ b/content/browser/service_worker/service_worker_cache.cc
@@ -9,6 +9,7 @@
 #include "base/files/file_path.h"
 #include "base/guid.h"
 #include "base/message_loop/message_loop_proxy.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/strings/string_util.h"
 #include "content/browser/service_worker/service_worker_cache.pb.h"
 #include "content/public/browser/browser_thread.h"
@@ -216,6 +217,11 @@ class ServiceWorkerCache::BlobReader : public net::URLRequest::Delegate {
   }
 
   void OnResponseStarted(net::URLRequest* request) override {
+    // TODO(vadimt): Remove ScopedTracker below once crbug.com/423948 is fixed.
+    tracked_objects::ScopedTracker tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "423948 ServiceWorkerCache::BlobReader::OnResponseStarted"));
+
     if (!request->status().is_success()) {
       callback_.Run(entry_.Pass(), false);
       return;
@@ -232,6 +238,11 @@ class ServiceWorkerCache::BlobReader : public net::URLRequest::Delegate {
   }
 
   void OnReadCompleted(net::URLRequest* request, int bytes_read) override {
+    // TODO(vadimt): Remove ScopedTracker below once crbug.com/423948 is fixed.
+    tracked_objects::ScopedTracker tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "423948 ServiceWorkerCache::BlobReader::OnReadCompleted"));
+
     if (!request->status().is_success()) {
       callback_.Run(entry_.Pass(), false);
       return;