cc: Allow activating to something other than high-res

If the pending tree is only allowed to activate when it has all of its
high res visible tiles ready to draw, then this can starve activation in
cases where the pending tree could have activated earlier without a
flash.

The fix is that when the active tree has high res tiles that are not
ready to draw or are shared with the pending tree, then the pending tree
does not need those tiles to be ready before activating.  To compensate
for not needing high res tiles, the pending tree may need to require low
res tiles if the active tree is drawing its low res tiles.  This
strategy allows faster activation during scrolling when both the active
and pending tree may be checkerboarding or showing low res.

Pending layers are still not allowed to activate with no content if the
active layer does not exist or if the active layer has no tilings (i.e.
didn't draw any content on previous frames).  This prevents newly
visible layers from activating without their content ready (which would
cause the content to incrementally appear over several frames in a
visually unappealing way).

BUG=315180

Review URL: https://codereview.chromium.org/75883002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237385 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 1 insertions, 1 deletions

diff --git a/cc/test/fake_picture_layer_tiling_client.cc b/cc/test/fake_picture_layer_tiling_client.cc
index 597e0d8..7ebd179 100644
--- a/cc/test/fake_picture_layer_tiling_client.cc
+++ b/cc/test/fake_picture_layer_tiling_client.cc
@@ -63,7 +63,7 @@ const Region* FakePictureLayerTilingClient::GetInvalidation() {
 }
 
 const PictureLayerTiling* FakePictureLayerTilingClient::GetTwinTiling(
-      const PictureLayerTiling* tiling) {
+      const PictureLayerTiling* tiling) const {
   return twin_tiling_;
 }