cc/blimp: Add synchronization for scroll/scale state.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 323 matching lines @@
   if (compositor_frame_sink_)
     compositor_frame_sink_->ForceReclaimResources();
 
   if (!CommitToActiveTree())
     CreatePendingTree();
 }
 
 void LayerTreeHostImpl::CommitComplete() {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::CommitComplete");
 
+  // If the state was committed to the pending tree, apply any reflected deltas

[danakj, 2016/10/25 22:14:43]

sync tree

[Khushal, 2016/10/26 01:03:29]

Done.

+  // that were not applied on the main thread.

[danakj, 2016/10/25 22:14:43]

applied during the main frame

[Khushal, 2016/10/26 01:03:29]

Done.

+  if (pending_tree())
+    pending_tree()->ApplyReflectedMainFrameState();

[danakj, 2016/10/25 22:14:43]

Shouldn't it do this on the sync tree always?

[Khushal, 2016/10/25 22:44:33]

Hmmm, if I copy to the pending base here, I don't think it will work. Looking at
the example of page scale, we PushFromMainThread during commit, and when
committing to the active tree, PushPendingToActive in the same call. And since
this happens post commit, the value will never make it to the active tree in
that mode.

I could probably check in LayerTreeImpl when over-writing the value. If its the
active tree, add the delta to the active base, otherwise the pending base. How
does that sound?

[danakj, 2016/10/25 23:55:55]

That sounds ok I think. If this sounds like complexity you won't use then maybe
this condition should be (!CommitToActive()) to show that intent more clearly
and DCHECK that otherwise its always empty unapplied stuff or something.

[Khushal, 2016/10/26 01:03:29]

Its not that complex to do, but we won't use it. So I avoided it. Added some
DCHECKs to make sure only the pending tree gets this state.

+
   if (CommitToActiveTree()) {
     // We have to activate animations here or "IsActive()" is true on the layers
     // but the animations aren't activated yet so they get ignored by
     // UpdateDrawProperties.
     ActivateAnimations();
   }
 
   // Start animations before UpdateDrawProperties and PrepareTiles, as they can
   // change the results. When doing commit to the active tree, this must happen
   // after ActivateAnimations() in order for this ticking to be propogated to
@@ skipping 3748 matching lines @@
   if (is_visible) {
     worker_context_visibility_ =
         worker_context->CacheController()->ClientBecameVisible();
   } else {
     worker_context->CacheController()->ClientBecameNotVisible(
         std::move(worker_context_visibility_));
   }
 }
 
 }  // namespace cc