cc: Replace Region with SimpleEnclosedRegion for occlusion tracking

Instead of using an arbitrary Region, which is costly (slow), use
a new SimpleEnclosedRegion. This class tracks only a single Rect
at a given time so it is very fast and small. It tries to get
something like the largest rect enclosed in the actual Region
(were we to track such a Region) in an online fashion, ie it
doesn't remember anything except its current largest possible
rect.

BUG=405663

Review URL: https://codereview.chromium.org/202523002

Cr-Commit-Position: refs/heads/master@{#291292}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@291292 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 4 insertions, 3 deletions

diff --git a/cc/layers/tiled_layer.cc b/cc/layers/tiled_layer.cc
index c1937e4..4a960a8 100644
--- a/cc/layers/tiled_layer.cc
+++ b/cc/layers/tiled_layer.cc
@@ -10,6 +10,7 @@
 #include "base/auto_reset.h"
 #include "base/basictypes.h"
 #include "build/build_config.h"
+#include "cc/base/simple_enclosed_region.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/tiled_layer_impl.h"
 #include "cc/resources/layer_updater.h"
@@ -639,11 +640,11 @@ void TiledLayer::SetTexturePriorities(const PriorityCalculator& priority_calc) {
   }
 }
 
-Region TiledLayer::VisibleContentOpaqueRegion() const {
+SimpleEnclosedRegion TiledLayer::VisibleContentOpaqueRegion() const {
   if (skips_draw_)
-    return Region();
+    return SimpleEnclosedRegion();
   if (contents_opaque())
-    return visible_content_rect();
+    return SimpleEnclosedRegion(visible_content_rect());
   return tiler_->OpaqueRegionInContentRect(visible_content_rect());
 }