[Mac] Maximise timer slack for background tabs

chrome/browser/resource_throttle.cc

+// Copyright (c) 2014 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/resource_throttle.h"
+
+#include "chrome/browser/media/audio_stream_monitor.h"
+#include "chrome/common/render_messages.h"
+#include "content/public/browser/render_frame_host.h"
+
+DEFINE_WEB_CONTENTS_USER_DATA_KEY(ResourceThrottle);
+
+ResourceThrottle::~ResourceThrottle() {
+  MediaCaptureDevicesDispatcher::GetInstance()->RemoveObserver(this);
+}
+
+ResourceThrottle::ResourceThrottle(content::WebContents* contents)
+    : timer_coalescing_enabled_(false) {
+  contents_ = contents;
+  Observe(contents);
+  MediaCaptureDevicesDispatcher::GetInstance()->AddObserver(this);
+}
+
+void ResourceThrottle::WasShown() {
+  SetTimerCoalescingEnabled(false);
+}
+
+void ResourceThrottle::WasHidden() {
+  AudioStreamMonitor* const audio_stream_monitor =
+      AudioStreamMonitor::FromWebContents(contents_);
+  bool was_recently_audible =
+      audio_stream_monitor && audio_stream_monitor->WasRecentlyAudible();
+
+  if (!was_recently_audible)
+    SetTimerCoalescingEnabled(true);
+}
+
+void ResourceThrottle::OnCreatingAudioStream(int render_process_id,

[aiolos (Not reviewing), 2014/05/20 17:45:23]

Were you planning on using OnAudioStreamPlaying/OnAudioStreamStopped as signals
as well?

+                                             int render_frame_id) {
+  // Check that the frame in question is the one we're tracking.
+  content::RenderFrameHost* render_frame_host =
+      content::RenderFrameHost::FromID(render_process_id, render_frame_id);
+  content::WebContents* tab =
+      content::WebContents::FromRenderFrameHost(render_frame_host);
+  if (tab != contents_)
+    return;
+
+  SetTimerCoalescingEnabled(false);
+}
+
+void ResourceThrottle::SetTimerCoalescingEnabled(bool enabled) {
+  if (timer_coalescing_enabled_ == enabled)
+    return;
+  Send(new ChromeViewMsg_SetCoalesceTimers(enabled));
+  timer_coalescing_enabled_ = enabled;
+}