Isolate tiling clip state from snapshot

bug:8409891

Snapshots frequently have their clip overwritten due to applying
deferred state - now, store tiling clip information in a separate
rect, outside of the snapshot so it isn't overwritten.

Change-Id: I21ca4c45dcd802eae99e8de86f11525196777ccb
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index 71bd6bb..7bb9395 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -947,7 +947,7 @@
     // Current state
     sp<Snapshot> mSnapshot;
     // State used to define the clipping region
-    sp<Snapshot> mTilingSnapshot;
+    Rect mTilingClip;
 
     // Used to draw textured quads
     TextureVertex mMeshVertices[4];