Apply PIP mask correctly to second (and later) PIP window

Previously the mask was applied only to the first PIP window. This CL
fixes this bug.

Bug: 902637
Test: Tested manually with the steps on the issue
Test: Added test passes

Change-Id: I4f86fa1713a861243ab3c87d051ff491f7b6bd32
Reviewed-on: https://chromium-review.googlesource.com/c/1322188Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609924}

ash/wm/window_state.cc

@@ -868,5 +868,14 @@ void WindowState::OnWindowDestroying(aura::Window* window) {
   delegate_.reset();
 }
 
+void WindowState::OnWindowLayerRecreated(aura::Window* window) {
+  DCHECK_EQ(window_, window);
+  // THe mask layer will be moved with old layer.
+  DCHECK(!window_->layer()->layer_mask_layer());
+  pip_mask_.reset();
+  if (IsPip())
+    UpdatePipRoundedCorners();
+}
+
 }  // namespace wm
 }  // namespace ash

ash/wm/window_state.h

@@ -361,6 +361,7 @@ class ASH_EXPORT WindowState : public aura::WindowObserver {
   FRIEND_TEST_ALL_PREFIXES(WindowAnimationsTest, CrossFadeToBounds);
   FRIEND_TEST_ALL_PREFIXES(WindowAnimationsTest,
                            CrossFadeToBoundsFromTransform);
+  FRIEND_TEST_ALL_PREFIXES(WindowStateTest, PipWindowMaskRecreated);
   FRIEND_TEST_ALL_PREFIXES(WindowStateTest, PipWindowHasMaskLayer);
 
   // Class to host the rounded mask for PIP windows.
@@ -435,6 +436,7 @@ class ASH_EXPORT WindowState : public aura::WindowObserver {
                                intptr_t old) override;
   void OnWindowAddedToRootWindow(aura::Window* window) override;
   void OnWindowDestroying(aura::Window* window) override;
+  void OnWindowLayerRecreated(aura::Window* window) override;
 
   // The owner of this window settings.
   aura::Window* window_;

ash/wm/window_state_unittest.cc

@@ -173,6 +173,31 @@ TEST_F(WindowStateTest, PipWindowCannotSnap) {
   EXPECT_FALSE(window_state->CanSnap());
 }
 
+// Test that a mask layer is created correctly.
+TEST_F(WindowStateTest, PipWindowMaskRecreated) {
+  // Prepare a PIP window.
+  std::unique_ptr<aura::Window> window(
+      CreateTestWindowInShellWithBounds(gfx::Rect(100, 100, 100, 100)));
+  WindowState* window_state = GetWindowState(window.get());
+  window_state->SetStateObject(std::unique_ptr<WindowState::State>(
+      new InitialStateTestState(mojom::WindowStateType::PIP)));
+  window_state->UpdatePipRoundedCorners();
+
+  // Mask layer exists.
+  EXPECT_TRUE(window->layer());
+  EXPECT_TRUE(window->layer()->layer_mask_layer());
+
+  // Close the PIP window.
+  window->Hide();
+
+  // Reshow the PIP window.
+  window->Show();
+
+  // Confirms a mask layer exists.
+  EXPECT_TRUE(window->layer());
+  EXPECT_TRUE(window->layer()->layer_mask_layer());
+}
+
 // Test that a PIP window cannot be snapped.
 TEST_F(WindowStateTest, PipWindowHasMaskLayer) {
   // Prepare a PIP window.