cc: Allow layers to have tilings even if twin doesn't

This fixes a bug where an active layer has a valid raster scale but
can't have tilings.  When a pending layer that could have tilings syncs
to it, it picks up these raster scales and so doesn't think it needs to
change tilings, even though it doesn't have any.  Worse, this state
would continue to persist for every future pending layer that can have
tilings because they would also pick up these raster scales without
tilings and think they were in an acceptable state.

This patch addresses this problem by always making sure that raster
scales are reset whenever a layer can't have tilings.  This causes
PictureLayerImpl::ManageTilings to not early out and to create new
tilings as soon as it is possible.

R=danakj@chromium.org
BUG=313598

Review URL: https://codereview.chromium.org/78853006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236716 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 19 insertions, 4 deletions

diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 9aaad29..29f5110 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -383,7 +383,7 @@ void PictureLayerImpl::DidBeginTracing() {
 
 void PictureLayerImpl::DidLoseOutputSurface() {
   if (tilings_)
-    tilings_->RemoveAllTilings();
+    RemoveAllTilings();
 
   ResetRasterScale();
 }
@@ -553,8 +553,7 @@ void PictureLayerImpl::SyncFromActiveLayer(const PictureLayerImpl* other) {
   UpdateLCDTextStatus(other->is_using_lcd_text_);
 
   if (!DrawsContent()) {
-    ResetRasterScale();
-    tilings_->RemoveAllTilings();
+    RemoveAllTilings();
     return;
   }
 
@@ -597,7 +596,7 @@ void PictureLayerImpl::SyncFromActiveLayer(const PictureLayerImpl* other) {
                           tiling_invalidation,
                           MinimumContentsScale());
   } else {
-    tilings_->RemoveAllTilings();
+    RemoveAllTilings();
   }
 
   SanityCheckTilingState();
@@ -778,9 +777,17 @@ void PictureLayerImpl::RemoveTiling(float contents_scale) {
       break;
     }
   }
+  if (tilings_->num_tilings() == 0)
+    ResetRasterScale();
   SanityCheckTilingState();
 }
 
+void PictureLayerImpl::RemoveAllTilings() {
+  tilings_->RemoveAllTilings();
+  // If there are no tilings, then raster scales are no longer meaningful.
+  ResetRasterScale();
+}
+
 namespace {
 
 inline float PositiveRatio(float float1, float float2) {
@@ -807,6 +814,11 @@ void PictureLayerImpl::ManageTilings(bool animating_transform_to_screen) {
       low_res_raster_contents_scale_ == 0.f ||
       ShouldAdjustRasterScale(animating_transform_to_screen);
 
+  if (tilings_->num_tilings() == 0) {
+    DCHECK(change_target_tiling)
+        << "A layer with no tilings shouldn't have valid raster scales";
+  }
+
   // Store the value for the next time ShouldAdjustRasterScale is called.
   raster_source_scale_was_animating_ = animating_transform_to_screen;
 
@@ -931,6 +943,8 @@ void PictureLayerImpl::CalculateRasterContentsScale(
 void PictureLayerImpl::CleanUpTilingsOnActiveLayer(
     std::vector<PictureLayerTiling*> used_tilings) {
   DCHECK(layer_tree_impl()->IsActiveTree());
+  if (tilings_->num_tilings() == 0)
+    return;
 
   float min_acceptable_high_res_scale = std::min(
       raster_contents_scale_, ideal_contents_scale_);
@@ -974,6 +988,7 @@ void PictureLayerImpl::CleanUpTilingsOnActiveLayer(
       twin->RemoveTiling(to_remove[i]->contents_scale());
     tilings_->Remove(to_remove[i]);
   }
+  DCHECK_GT(tilings_->num_tilings(), 0u);
 
   SanityCheckTilingState();
 }