cc: Define Region::Contains() to be A contains B if all points in B are also in A.

cc/occlusion_tracker.cc

Index: cc/occlusion_tracker.cc
diff --git a/cc/occlusion_tracker.cc b/cc/occlusion_tracker.cc
index 50a453e186cfc4e4eaa461446ac35361cc03a750..9c536d2e3a29e8977cdff3f1da09771eb5563edb 100644
--- a/cc/occlusion_tracker.cc
+++ b/cc/occlusion_tracker.cc
@@ -314,7 +314,7 @@ static inline bool testContentRectOccluded(const gfx::Rect& contentRect, const W
     gfx::RectF transformedRect = MathUtil::mapClippedRect(contentSpaceTransform, gfx::RectF(contentRect));
     // Take the gfx::ToEnclosingRect, as we want to include partial pixels in the test.
     gfx::Rect targetRect = gfx::IntersectRects(gfx::ToEnclosingRect(transformedRect), clipRectInTarget);
-    return targetRect.IsEmpty() || occlusion.Contains(targetRect);
+    return occlusion.Contains(targetRect);
 }
 
 template<typename LayerType, typename RenderSurfaceType>