Fix layer blending bug

Cached layers were sometimes retaining an obsolete blending
value, causing artifacts where translucent objects were disappearing
completely. Also, added extra tracing info for DisplayLists.

Issue #6303668 Flickering views during SwipeHelper drag

Change-Id: I66ce158652c4a3ed316040585b40b1744e1fad0c
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index b52d2b0..47927bb 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -101,6 +101,7 @@
     ANDROID_API const Rect& getClipBounds();
     ANDROID_API bool quickReject(float left, float top, float right, float bottom);
     virtual bool clipRect(float left, float top, float right, float bottom, SkRegion::Op op);
+    virtual Rect* getClipRect();
 
     virtual status_t drawDisplayList(DisplayList* displayList, uint32_t width, uint32_t height,
             Rect& dirty, int32_t flags, uint32_t level = 0);