Fix SetShape (SetAlphaShape) to allow Null regions (+ tests).

ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc
index 8a66c6e032717e46a21ab5390aaa305c76b6565a..2e9188a6b3df0582fa90fb41b67842bae6fdb933 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc
@@ -307,6 +307,17 @@ TEST_F(DesktopWindowTreeHostX11Test, Shape) {
   EXPECT_TRUE(ShapeRectContainsPoint(shape_rects, 15, 5));
   EXPECT_TRUE(ShapeRectContainsPoint(shape_rects, 95, 15));
   EXPECT_FALSE(ShapeRectContainsPoint(shape_rects, 105, 15));
+
+  // Setting the shape to NULL resets the shape back to the entire
+  // window bounds.
+  widget2->SetShape(NULL);
+  shape_rects = GetShapeRects(xid2);
+  ASSERT_FALSE(shape_rects.empty());
+  EXPECT_TRUE(ShapeRectContainsPoint(shape_rects, 5, 5));
+  EXPECT_TRUE(ShapeRectContainsPoint(shape_rects, 15, 5));
+  EXPECT_TRUE(ShapeRectContainsPoint(shape_rects, 95, 15));
+  EXPECT_TRUE(ShapeRectContainsPoint(shape_rects, 105, 15));
+  EXPECT_FALSE(ShapeRectContainsPoint(shape_rects, 500, 500));
 }
 
 // Test that the widget ignores changes in fullscreen state initiated by the