android: Reset input connection on detach

BaseInputConnection will keep a reference to the container view, which
causes leaks after onDetachedFromWindow.

Bug: 1149336
Change-Id: Iee7683092ea6f8878a09de78a09d044d8d29d246
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536785
Commit-Queue: Changwan Ryu <changwan@chromium.org>
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Auto-Submit: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827959}

content/public/android/java/src/org/chromium/content/browser/input/ThreadedInputConnectionFactory.java

@@ -310,5 +310,6 @@ public class ThreadedInputConnectionFactory implements ChromiumBaseInputConnecti
         if (DEBUG_LOGS) Log.d(TAG, "onViewDetachedFromWindow");
         if (mCheckInvalidator != null) mCheckInvalidator.invalidate();
         if (mProxyView != null) mProxyView.onOriginalViewDetachedFromWindow();
+        mThreadedInputConnection = null;
     }
 }