SurfaceFlinger: add a crop to the layer state

This change adds a crop rectangle specified in window coordinates to the layer
state.  The all window pixels outside this crop rectangle are treated as though
they were fully transparent.  This change also adds the plumbing necessary for
WindowManager to set that crop.

Change-Id: I582bc445dc8c97d4c943d4db8d582a6ef5a66081
diff --git a/include/gui/SurfaceComposerClient.h b/include/gui/SurfaceComposerClient.h
index d971031..3bd10de 100644
--- a/include/gui/SurfaceComposerClient.h
+++ b/include/gui/SurfaceComposerClient.h
@@ -127,6 +127,7 @@
     status_t    setMatrix(SurfaceID id, float dsdx, float dtdx, float dsdy, float dtdy);
     status_t    setPosition(SurfaceID id, float x, float y);
     status_t    setSize(SurfaceID id, uint32_t w, uint32_t h);
+    status_t    setCrop(SurfaceID id, const Rect& crop);
     status_t    destroySurface(SurfaceID sid);
 
 private: