Speculative fix for Android moveTaskToBack framework bug.

BUG=817567

Change-Id: Ic9c599df1b2e3245b1d480cea29271c8d0f673a8
Reviewed-on: https://chromium-review.googlesource.com/956253Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542163}

chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java

@@ -1962,6 +1962,17 @@ public class ChromeTabbedActivity
         }
     }
 
+    @Override
+    public boolean moveTaskToBack(boolean nonRoot) {
+        try {
+            return super.moveTaskToBack(nonRoot);
+        } catch (NullPointerException e) {
+            // Work around framework bug described in https://crbug.com/817567.
+            finish();
+            return true;
+        }
+    }
+
     /**
      * Launch a URL from an intent.
      *