Mac: Fix janky YouTube animations

content/browser/renderer_host/compositing_iosurface_layer_mac.mm

Index: content/browser/renderer_host/compositing_iosurface_layer_mac.mm
diff --git a/content/browser/renderer_host/compositing_iosurface_layer_mac.mm b/content/browser/renderer_host/compositing_iosurface_layer_mac.mm
index 8efa2589f1e9045fe8405065ffba84ad6a589fdc..35cee20155c840e8d07fc2c97f224269eda28046 100644
--- a/content/browser/renderer_host/compositing_iosurface_layer_mac.mm
+++ b/content/browser/renderer_host/compositing_iosurface_layer_mac.mm
@@ -54,7 +54,7 @@ void CompositingIOSurfaceLayerHelper::GotNewFrame() {
   // If reqested, draw immediately and don't bother trying to use the
   // isAsynchronous property to ensure smooth animation.
   if (client_->AcceleratedLayerShouldAckImmediately()) {
-    ImmediatelyForceDisplayAndAck();
+    SetNeedsDisplayAndDisplayAndAck();
   } else {
     if (![layer_ isAsynchronous])
       [layer_ setAsynchronous:YES];
@@ -104,8 +104,29 @@ void CompositingIOSurfaceLayerHelper::AckPendingFrame(bool success) {
   TRACE_COUNTER_ID1("browser", "PendingSwapAck", this, 0);
 }
 
-void CompositingIOSurfaceLayerHelper::ImmediatelyForceDisplayAndAck() {
+void CompositingIOSurfaceLayerHelper::SetNeedsDisplayAndDisplayAndAck() {
+  // Drawing using setNeedsDisplay and displayIfNeeded will result in
+  // subsequent canDrawInCGLContext callbacks getting dropped, and jerky
+  // animation. Disable asynchronous drawing before issuing these calls as a
+  // workaround.
+  // http://crbug.com/395827
+  if ([layer_ isAsynchronous])
+    [layer_ setAsynchronous:NO];

[Ken Russell (switch to Gerrit), 2014/07/22 19:52:04]

I don't know the various state transitions done to this layer; who sets it back
to asynchronous? If we're in the middle of a scroll (is the layer in async mode
then?) and for some reason we have to display a frame immediately, will the
scroll be aborted abruptly?

[ccameron, 2014/07/23 07:50:34]

It gets re-set to asynchronous as soon as a new frame from the renderer comes
in. The asynchronous mode is a way of making animation smooth -- the synchronous
mode works fine in terms of making forward progress, but can be janky. In these
situations (where we're forcing a display), we're prioritizing getting a frame
up over smoothness (it may be that we'll want to push this prioritization down
to the renderer too, but that's for another day).

+
   [layer_ setNeedsDisplay];
+  DisplayIfNeededAndAck();
+}
+
+void CompositingIOSurfaceLayerHelper::DisplayIfNeededAndAck() {
+  if (!needs_display_)
+    return;
+
+  // As in SetNeedsDisplayAndDisplayAndAck, disable asynchronous drawing before
+  // issuing displayIfNeeded.
+  // http://crbug.com/395827
+  if ([layer_ isAsynchronous])
+    [layer_ setAsynchronous:NO];
+
   [layer_ displayIfNeeded];
 
   // Calls to setNeedsDisplay can sometimes be ignored, especially if issued
@@ -116,7 +137,7 @@ void CompositingIOSurfaceLayerHelper::ImmediatelyForceDisplayAndAck() {
 }
 
 void CompositingIOSurfaceLayerHelper::TimerFired() {
-  ImmediatelyForceDisplayAndAck();
+  SetNeedsDisplayAndDisplayAndAck();
 }
 
 }  // namespace content
@@ -171,6 +192,14 @@ void CompositingIOSurfaceLayerHelper::TimerFired() {
   helper_->GotNewFrame();
 }
 
+- (void)setNeedsDisplayAndDisplayAndAck {
+  helper_->SetNeedsDisplayAndDisplayAndAck();
+}
+
+- (void)displayIfNeededAndAck {
+  helper_->DisplayIfNeededAndAck();
+}
+
 // The remaining methods implement the CAOpenGLLayer interface.
 
 - (CGLPixelFormatObj)copyCGLPixelFormatForDisplayMask:(uint32_t)mask {