Add new property to debug non-rectangular clip operations

This change adds a new property called "debug.hwui.show_stencil_clip"
that accepts the following values:

- "highlight", colorizes in green any drawing command that's tested
  against a non-rectangular clip region
- "region", shows the non-rectangular clip region in blue every time
  it is used
- "hide", default value, nothing is shown

Change-Id: I83c8602310edc4aaeb8b905371cdd185b17d32b5
diff --git a/libs/hwui/Caches.h b/libs/hwui/Caches.h
index 0ca2ffd..c35ad883 100644
--- a/libs/hwui/Caches.h
+++ b/libs/hwui/Caches.h
@@ -245,9 +245,18 @@
 
     // Misc
     GLint maxTextureSize;
+
+    // Debugging
     bool debugLayersUpdates;
     bool debugOverdraw;
 
+    enum StencilClipDebug {
+        kStencilHide,
+        kStencilShowHighlight,
+        kStencilShowRegion
+    };
+    StencilClipDebug debugStencilClip;
+
     TextureCache textureCache;
     LayerCache layerCache;
     RenderBufferCache renderBufferCache;