Tessellate on worker threads

Tessellate and cache (where possible) shadow and round rect
tessellation tasks.

Change-Id: I2cfda8e11d83d51ea74af871235cf26e8f831d40
diff --git a/libs/hwui/Rect.h b/libs/hwui/Rect.h
index 2ddbbd7..846ebdc 100644
--- a/libs/hwui/Rect.h
+++ b/libs/hwui/Rect.h
@@ -186,6 +186,13 @@
         bottom += delta;
     }
 
+    void outset(float xdelta, float ydelta) {
+        left -= xdelta;
+        top -= ydelta;
+        right += xdelta;
+        bottom += ydelta;
+    }
+
     /**
      * Similar to snapToPixelBoundaries, but estimates bounds conservatively to handle GL rounding
      * errors.