Android: fix crash when closing browser during text selection

Bug: 1160320
Change-Id: I49f31f5a6044024d0c36bea0eb4caf8251440210
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2598331
Commit-Queue: Bo <boliu@chromium.org>
Auto-Submit: Evan Stade <estade@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840156}

content/public/android/java/src/org/chromium/content/browser/selection/SmartSelectionMetricsLogger.java

@@ -37,6 +37,7 @@ public class SmartSelectionMetricsLogger implements SelectionMetricsLogger {
     private static final String TAG = "SmartSelectionLogger";
     private static final boolean DEBUG = false;
 
+    // May be null if {@link onWindowAndroidChanged()} sets it to null.
     private WindowAndroid mWindowAndroid;
 
     private TextClassifier mSession;
@@ -64,6 +65,8 @@ public class SmartSelectionMetricsLogger implements SelectionMetricsLogger {
     }
 
     public void logSelectionStarted(String selectionText, int startOffset, boolean editable) {
+        if (mWindowAndroid == null) return;
+
         Context context = mWindowAndroid.getContext().get();
         if (context == null) return;