Skip drawing offscreen objects

Previous logic in ViewRoot would schedule and perform a draw
when it was requested by offscreen objects. The problem was that the
logic checking for an interesection between the offscreen invalidation rectangle
and the onscreen display rectangle was flawed. The fix was to use the return value
from Rect.intersect() to do the right thing and skip drawing.

Issue #7366568 Offscreen invalidates can cause useless work for framework

Change-Id: Ie4e277c695dacee39848a8a223f0c4ee34d9bb4d

core/java/android/view/ViewRootImpl.java

@@ -887,11 +887,12 @@ public final class ViewRootImpl implements ViewParent,
         // Intersect with the bounds of the window to skip
         // updates that lie outside of the visible region
         final float appScale = mAttachInfo.mApplicationScale;
-        localDirty.intersect(0, 0,
-                (int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f));
-
-        if (!mWillDrawSoon) {
+        if (localDirty.intersect(0, 0,
+                (int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f)) &&
+                !mWillDrawSoon) {
             scheduleTraversals();
+        } else {
+            localDirty.setEmpty();
         }
 
         return null;