Fix crash in DisplayCutoutController

Bug: 1107361
Change-Id: I6e5413b8c717690d04a078001ed93b61a64447b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2307691Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790038}

chrome/android/java/src/org/chromium/chrome/browser/display_cutout/DisplayCutoutController.java

@@ -204,7 +204,7 @@ public class DisplayCutoutController implements InsetObserverView.WindowInsetObs
 
     @VisibleForTesting
     protected LayoutParams getWindowAttributes() {
-        return mWindow.getAttributes();
+        return mWindow == null ? null : mWindow.getAttributes();
     }
 
     @VisibleForTesting
@@ -218,6 +218,8 @@ public class DisplayCutoutController implements InsetObserverView.WindowInsetObs
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.P) return;
 
         LayoutParams attributes = getWindowAttributes();
+        if (attributes == null) return;
+
         attributes.layoutInDisplayCutoutMode = getDisplayCutoutMode();
         setWindowAttributes(attributes);
     }

chrome/android/junit/src/org/chromium/chrome/browser/display_cutout/DisplayCutoutControllerTest.java

@@ -197,6 +197,18 @@ public class DisplayCutoutControllerTest {
         verify(mWindow).getAttributes();
     }
 
+    @Test
+    @SmallTest
+    public void testLayout_NoWindow() {
+        // Verify there's no crash when the tab's interactability changes after activity detachment.
+        verify(mTab).addObserver(mTabObserverCaptor.capture());
+        reset(mTab);
+
+        mTabObserverCaptor.getValue().onActivityAttachmentChanged(mTab, null);
+        mTabObserverCaptor.getValue().onInteractabilityChanged(mTab, false);
+        verify(mWindow, never()).getAttributes();
+    }
+
     @Test
     @SmallTest
     public void testLayoutOnShown() {