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

cc/region.cc

Index: cc/region.cc
diff --git a/cc/region.cc b/cc/region.cc
index 7a5e83cd60fbce38d8f627c82f90fc06ce9e2cae..f0fddc5857b1f5c5e91a638f8e6f3ca379e9e9c2 100644
--- a/cc/region.cc
+++ b/cc/region.cc
@@ -47,10 +47,14 @@ bool Region::Contains(gfx::Point point) const {
 }
 
 bool Region::Contains(gfx::Rect rect) const {
+  if (rect.IsEmpty())
+    return true;
   return skregion_.contains(ToSkIRect(rect));
 }
 
 bool Region::Contains(const Region& region) const {
+  if (region.IsEmpty())
+    return true;
   return skregion_.contains(region.skregion_);
 }