Adding instrumentation to locate the source of jankiness.

chrome/browser/task_manager/task_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/task_manager/task_manager.h"
 
 #include "base/bind.h"
 #include "base/i18n/number_formatting.h"
 #include "base/i18n/rtl.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/process/process_metrics.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/stl_util.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/profiles/profile_window.h"
 #include "chrome/browser/task_manager/background_information.h"
 #include "chrome/browser/task_manager/browser_process_resource_provider.h"
@@ skipping 1199 matching lines @@
   for (ResourceList::iterator it = resources_.begin();
        it != resources_.end(); ++it) {
     if (base::GetProcId((*it)->GetProcess()) == renderer_id) {
       (*it)->NotifyV8HeapStats(v8_memory_allocated, v8_memory_used);
     }
   }
 }
 
 void TaskManagerModel::NotifyBytesRead(const net::URLRequest& request,
                                        int byte_count) {
+  // TODO(vadimt): Remove ScopedTracker below once crbug.com/423948 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "423948 TaskManagerModel::NotifyBytesRead"));

[mmenke, 2014/11/17 15:38:16]

I suggest adding another one just above the bytes_read_buffer_.push_back call. 
That seems the most likely culprit for OnRawBytesRead.

[vadimt, 2014/11/18 01:14:27]

Done.

+
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   if (!is_updating_byte_count_)
     return;
 
   // Only net::URLRequestJob instances created by the ResourceDispatcherHost
   // have an associated ResourceRequestInfo and a render frame associated.
   // All other jobs will have -1 returned for the render process child and
   // routing ids - the jobs may still match a resource based on their origin id,
   // otherwise BytesRead() will attribute the activity to the Browser resource.
   const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(&request);
@@ skipping 302 matching lines @@
   params.host_desktop_type = desktop_type;
   chrome::Navigate(&params);
 }
 
 TaskManager::TaskManager()
     : model_(new TaskManagerModel(this)) {
 }
 
 TaskManager::~TaskManager() {
 }