Adding instrumentation to locate the source of jankiness.

net/url_request/url_request_simple_job.cc

Index: net/url_request/url_request_simple_job.cc
diff --git a/net/url_request/url_request_simple_job.cc b/net/url_request/url_request_simple_job.cc
index f266e3b505d05ea37b7e237ce91e8dbc472c0937..a02da27d2611575585fdcdb037cc11ebf3e67eff 100644
--- a/net/url_request/url_request_simple_job.cc
+++ b/net/url_request/url_request_simple_job.cc
@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/message_loop/message_loop.h"
+#include "base/profiler/scoped_profile.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_request_headers.h"
@@ -60,6 +61,11 @@ void URLRequestSimpleJob::StartAsync() {
     return;
 
   if (ranges().size() > 1) {
+    // TODO(vadimt): Remove ScopedProfile below once crbug.com/422489 is fixed.
+    tracked_objects::ScopedProfile tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "422489 URLRequestSimpleJob::StartAsync 1"));
+
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED,
                                 ERR_REQUEST_RANGE_NOT_SATISFIABLE));
     return;
@@ -68,11 +74,29 @@ void URLRequestSimpleJob::StartAsync() {
   if (!ranges().empty() && range_parse_result() == OK)
     byte_range_ = ranges().front();
 
-  int result = GetData(&mime_type_, &charset_, &data_,
-                       base::Bind(&URLRequestSimpleJob::OnGetDataCompleted,
-                                  weak_factory_.GetWeakPtr()));
-  if (result != ERR_IO_PENDING)
+  int result;
+  {
+    // TODO(vadimt): Remove ScopedProfile below once crbug.com/422489 is fixed.
+    // Remove the block and assign 'result' in its declaration.
+    tracked_objects::ScopedProfile tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "422489 URLRequestSimpleJob::StartAsync 2"));
+
+    result = GetData(&mime_type_,
+                     &charset_,
+                     &data_,
+                     base::Bind(&URLRequestSimpleJob::OnGetDataCompleted,
+                                weak_factory_.GetWeakPtr()));
+  }
+
+  if (result != ERR_IO_PENDING) {
+    // TODO(vadimt): Remove ScopedProfile below once crbug.com/422489 is fixed.
+    tracked_objects::ScopedProfile tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "422489 URLRequestSimpleJob::StartAsync 3"));
+
     OnGetDataCompleted(result);
+  }
 }
 
 void URLRequestSimpleJob::OnGetDataCompleted(int result) {