cc: Consider visible rect for update tile priority early out.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index fd8a50772a6372fc9bf87184205683a4e89f5edd..243bd73b9616a86ce3ca5873bfe15f321c575a49 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -494,21 +494,6 @@ void PictureLayerImpl::UpdateTilePriorities(
 
   TRACE_EVENT0("cc", "PictureLayerImpl::UpdateTilePriorities");
 
-  double current_frame_time_in_seconds =
-      (layer_tree_impl()->CurrentBeginFrameArgs().frame_time -
-       base::TimeTicks()).InSecondsF();

[mithro-old, 2014/10/27 13:20:36]

Just a FYI, these lines will totally not do what you expect if called at the
wrong time. It's unclear to me when exactly this function is called, so I'm not
sure if that is possible?

When not in the background, the value of CurrentBeginFrameArgs is set in
WillBeginImplFrame and cleared by calling
ResetCurrentBeginFrameArgsForNextFrame.

When in the background this happens in the
LayerTreeHostImplTimeSourceAdapter::OnTimerTick() method.

When outside of the period between Update and Reset calls the
CurrentBeginFrameArgs method just returns Now().

All the above is kind of seriously horrible and really needs to be fixed. To
make matters even more confusing, this value won't match the the last vsync
value as it's overridden to now to preserve monotonicity guarantees caused by
returning Now() at other times! :(

Does the "NeedsUpdateForFrameAtTime" method depend on the frame time being
useful, or does it just need a monotonic increasing value?

-
-  bool tiling_needs_update = false;
-  for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
-    if (tilings_->tiling_at(i)->NeedsUpdateForFrameAtTime(
-            current_frame_time_in_seconds)) {
-      tiling_needs_update = true;
-      break;
-    }
-  }
-  if (!tiling_needs_update)
-    return;
-
   gfx::Rect viewport_rect_in_layer_space =
       GetViewportForTilePriorityInContentSpace();
   WhichTree tree =