Fix for internal bug below (crash when starting->pausing->disconnecting Cast)

Bug: internal/112284077
Change-Id: I4b61b81fa9ba5c6d97642b78504f56c1d6454738
Reviewed-on: https://chromium-review.googlesource.com/1182869
Commit-Queue: Andrei Pascovici <apascovici@chromium.org>
Reviewed-by: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584838}

chromecast/browser/android/apk/src/org/chromium/chromecast/shell/CastWebContentsView.java

@@ -77,7 +77,13 @@ class CastWebContentsView {
                     contentView, window, WebContents.createDefaultInternalsHolder());
             // Enable display of current webContents.
             webContents.onShow();
-            return webContents::onHide;
+            return () -> {
+                if (!webContents.isDestroyed()) {
+                    // WebContents can be destroyed by the app before CastWebContentsComponent
+                    // unbinds, which is why we need this check.
+                    webContents.onHide();
+                }
+            };
         };
     }
 }