Remove confusing behavior of Rect::intersect() and rename

bug:24670525

Removes silly 'do nothing if rects do not intersect' behavior, and
changes the name to clarify the difference (contrasting against
SkRect::intersect())

bug:24670525

Change-Id: Id2ca1cfea1a9d720d4dc70b251f426d9916f8b53
diff --git a/libs/hwui/LayerRenderer.cpp b/libs/hwui/LayerRenderer.cpp
index c63b559..227271d 100644
--- a/libs/hwui/LayerRenderer.cpp
+++ b/libs/hwui/LayerRenderer.cpp
@@ -58,7 +58,7 @@
         mLayer->region.clear();
         dirty.set(0.0f, 0.0f, width, height);
     } else {
-        dirty.intersect(0.0f, 0.0f, width, height);
+        dirty.doIntersect(0.0f, 0.0f, width, height);
         android::Rect r(dirty.left, dirty.top, dirty.right, dirty.bottom);
         mLayer->region.subtractSelf(r);
     }