cc: Replace Region with SimpleEnclosedRegion for occlusion tracking

cc/base/region.cc

Index: cc/base/region.cc
diff --git a/cc/base/region.cc b/cc/base/region.cc
index 79c30ec8251a0b0b881aed2ba304bbcc63eb64ba..2484cc21ecbe8da92993fa1a31067b03161ab1c7 100644
--- a/cc/base/region.cc
+++ b/cc/base/region.cc
@@ -3,8 +3,10 @@
 // found in the LICENSE file.
 
 #include "cc/base/region.h"
+
 #include "base/debug/trace_event_argument.h"
 #include "base/values.h"
+#include "cc/base/simple_enclosed_region.h"
 
 namespace cc {
 
@@ -80,6 +82,13 @@ void Region::Subtract(const Region& region) {
   skregion_.op(region.skregion_, SkRegion::kDifference_Op);
 }
 
+void Region::Subtract(const SimpleEnclosedRegion& region) {
+  for (size_t i = 0; i < region.GetRegionComplexity(); ++i) {
+    skregion_.op(gfx::RectToSkIRect(region.GetRect(i)),
+                 SkRegion::kDifference_Op);
+  }
+}
+
 void Region::Union(const gfx::Rect& rect) {
   skregion_.op(gfx::RectToSkIRect(rect), SkRegion::kUnion_Op);
 }