Shortcut a couple of IPCs when the task manager is disabled.

This saves about 6 idle wakeups on the top_10 idle energy benchmark. It can save up to 1/second in the general case.

BUG=411488

Review URL: https://codereview.chromium.org/542353002

Cr-Commit-Position: refs/heads/master@{#293813}

chrome/browser/task_manager/task_manager.cc

@@ -241,6 +241,7 @@ TaskManagerModel::TaskManagerModel(TaskManager* task_manager)
       update_requests_(0),
       listen_requests_(0),
       update_state_(IDLE),
+      is_updating_byte_count_(false),
       goat_salt_(base::RandUint64()) {
   AddResourceProvider(
       new task_manager::BrowserProcessResourceProvider(task_manager));
@@ -1055,6 +1056,10 @@ void TaskManagerModel::StartUpdating() {
     FOR_EACH_OBSERVER(TaskManagerModelObserver, observer_list_,
                       OnReadyPeriodicalUpdate());
   }
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      base::Bind(&TaskManagerModel::SetUpdatingByteCount, this, true));
 }
 
 void TaskManagerModel::StopUpdating() {
@@ -1070,6 +1075,10 @@ void TaskManagerModel::StopUpdating() {
 
   // Notify resource providers that we are done updating.
   StopListening();
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      base::Bind(&TaskManagerModel::SetUpdatingByteCount, this, false));
 }
 
 void TaskManagerModel::StartListening() {
@@ -1244,6 +1253,8 @@ void TaskManagerModel::NotifyV8HeapStats(base::ProcessId renderer_id,
 void TaskManagerModel::NotifyBytesRead(const net::URLRequest& request,
                                        int byte_count) {
   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.
@@ -1393,6 +1404,11 @@ void TaskManagerModel::NotifyMultipleBytesRead() {
                  base::Owned(bytes_read_buffer)));
 }
 
+void TaskManagerModel::SetUpdatingByteCount(bool is_updating) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  is_updating_byte_count_ = is_updating;
+}
+
 int64 TaskManagerModel::GetNetworkUsage(Resource* resource) const {
   int64 net_usage = GetNetworkUsageForResource(resource);
   if (net_usage == 0 && !resource->SupportNetworkUsage())

chrome/browser/task_manager/task_manager.h

@@ -450,6 +450,9 @@ class TaskManagerModel : public base::RefCountedThreadSafe<TaskManagerModel> {
   // for each one is expensive.
   void NotifyMultipleBytesRead();
 
+  // Called on the IO thread to start/stop updating byte counts.
+  void SetUpdatingByteCount(bool is_updating);
+
   // Returns the network usage (in byte per second) that should be displayed for
   // the passed |resource|.  -1 means the information is not available for that
   // resource.
@@ -533,6 +536,10 @@ class TaskManagerModel : public base::RefCountedThreadSafe<TaskManagerModel> {
   // Whether we are currently in the process of updating.
   UpdateState update_state_;
 
+  // Whether the IO thread is currently in the process of updating; accessed
+  // only on the IO thread.
+  bool is_updating_byte_count_;
+
   // A salt lick for the goats.
   uint64 goat_salt_;