Initialize ARect fields in default ctor

 So that we can use Rect() for update and such.

Bug: 18095940
Change-Id: I03ed87121d2d279f22013b75e95dd7254551ca1f
diff --git a/include/ui/Rect.h b/include/ui/Rect.h
index 6cf64eb..31e28d2 100644
--- a/include/ui/Rect.h
+++ b/include/ui/Rect.h
@@ -34,6 +34,7 @@
     // because we want the compiler generated versions
 
     inline Rect() {
+      left = right = top = bottom = 0;
     }
 
     inline Rect(int32_t w, int32_t h) {