Build layer damage bounds for shadows

bug:15538815

Change-Id: I703afeb7e31c28002bd1aff9ce448ec8cdc4e70d
diff --git a/libs/hwui/AmbientShadow.cpp b/libs/hwui/AmbientShadow.cpp
index 937b7c6..b9d7b12 100644
--- a/libs/hwui/AmbientShadow.cpp
+++ b/libs/hwui/AmbientShadow.cpp
@@ -136,6 +136,7 @@
         }
     }
     shadowVertexBuffer.setMode(mode);
+    shadowVertexBuffer.computeBounds<AlphaVertex>();
 
 #if DEBUG_SHADOW
     for (int i = 0; i < SHADOW_VERTEX_COUNT; i++) {