MacViews: Trigger shadow invalidation when a translucent window is shown.

Currently, invalidate_shadow_on_frame_swap_ is not set when a MacViews window is
shown. It is only set when the layer is created, changed or the window resized.
This causes translucent windows like the "Restore Pages" bubble and Find-In-Page
window to not have a shadow, when they are shown after being hidden.

This CL modifies BridgedNativeWidget::OnVisibilityChanged() to trigger shadow
invalidation while showing translucent windows. This fixes the shadow for the
"Restore Pages" bubble and also of the Find-In-Page window on tab switching. A
unit test is also added which demonstrates the problem.

Note that this does not fix the shadow for the Find-In-Page window when it is
displayed initially on pressing Cmd+F.

BUG=636707, 646734

Review-Url: https://codereview.chromium.org/2336983002
Cr-Commit-Position: refs/heads/master@{#418803}

ui/views/cocoa/bridged_native_widget.mm

@@ -839,6 +839,11 @@ void BridgedNativeWidget::OnVisibilityChanged() {
   if (layer()) {
     layer()->SetVisible(window_visible_);
     layer()->SchedulePaint(gfx::Rect(GetClientAreaSize()));
+
+    // For translucent windows which are made visible, recalculate shadow when
+    // the frame from the compositor arrives.
+    if (![window_ isOpaque])
+      invalidate_shadow_on_frame_swap_ = window_visible_;
   }
 
   NotifyVisibilityChangeDown();

ui/views/widget/native_widget_mac_unittest.mm

@@ -1376,6 +1376,17 @@ TEST_F(NativeWidgetMacTest, InvalidateShadow) {
   test_api.SimulateFrameSwap(gfx::Size(123, 456));
   EXPECT_EQ(2, [window invalidateShadowCount]);
 
+  // Hiding the window does not require shadow invalidation.
+  widget->Hide();
+  test_api.SimulateFrameSwap(gfx::Size(123, 456));
+  EXPECT_EQ(2, [window invalidateShadowCount]);
+
+  // Showing a translucent window after hiding it, should trigger shadow
+  // invalidation.
+  widget->Show();
+  test_api.SimulateFrameSwap(gfx::Size(123, 456));
+  EXPECT_EQ(3, [window invalidateShadowCount]);
+
   widget->CloseNow();
 }