Send idle notifications to V8 after commit

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index b9d7a019b13368dd617cd0a4601e0cf6c75e6aef..cbf28753c64fab063eb129b8bad3d074a7ae096d 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -38,6 +38,7 @@
 #include "third_party/WebKit/public/platform/WebCompositeAndReadbackAsyncCallback.h"
 #include "third_party/WebKit/public/platform/WebSelectionBound.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
+#include "third_party/WebKit/public/web/WebKit.h"
 #include "third_party/WebKit/public/web/WebWidget.h"
 #include "ui/gfx/frame_time.h"
 #include "ui/gl/gl_switches.h"
@@ -414,7 +415,12 @@ scoped_ptr<RenderWidgetCompositor> RenderWidgetCompositor::Create(
 RenderWidgetCompositor::RenderWidgetCompositor(RenderWidget* widget,
                                                bool threaded)
     : threaded_(threaded),
-      widget_(widget) {
+      widget_(widget),
+      send_v8_idle_notification_after_commit_(false) {
+  CommandLine* cmd = CommandLine::ForCurrentProcess();
+
+  if (cmd->HasSwitch(switches::kSendV8IdleNotificationAfterCommit))
+    send_v8_idle_notification_after_commit_ = true;
 }
 
 RenderWidgetCompositor::~RenderWidgetCompositor() {}
@@ -750,6 +756,8 @@ void RenderWidgetCompositor::DidBeginMainFrame() {
 }
 
 void RenderWidgetCompositor::BeginMainFrame(const cc::BeginFrameArgs& args) {
+  begin_main_frame_time_ = args.frame_time;
+  begin_main_frame_interval_ = args.interval;
   double frame_time = (args.frame_time - base::TimeTicks()).InSecondsF();
   WebBeginFrameArgs web_begin_frame_args = WebBeginFrameArgs(frame_time);
   widget_->webwidget()->beginFrame(web_begin_frame_args);
@@ -778,6 +786,15 @@ void RenderWidgetCompositor::WillCommit() {
 }
 
 void RenderWidgetCompositor::DidCommit() {
+  if (send_v8_idle_notification_after_commit_) {
+    int idle_time_in_ms =
+        std::max(0L, (begin_main_frame_time_ +
+                      begin_main_frame_interval_ -
+                      gfx::FrameTime::Now()).InMilliseconds());

[brianderson, 2014/08/26 19:05:41]

InMilliseconds() uses 64-bit division, which I understand is emulated or very
slow on some devices. It's only once per frame, so this may be completely
over-optimizing, but we might as well avoid it if we can.

Can you store the initial result in a base::TimeDelta and then only convert to
milliseconds if that result is > base::TimeDelta().

Then, to avoid the 64-bit division, convert the TimeDelta to *microseconds*
first, store that into a 32-bit value (which should be more than enough bits),
and then convert to milliseconds.

[ernstm, 2014/08/26 20:05:25]

Done.

+    if (idle_time_in_ms)
+      blink::mainThreadIsolate()->IdleNotification(idle_time_in_ms);
+  }
+
   widget_->DidCommitCompositorFrame();
   widget_->didBecomeReadyForAdditionalInput();
 }