Fix a snackbar crash about leaking window

chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarManager.java b/chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarManager.java
index 2cb0b0aeb34005f0df4e445c79a68a18c0a20739..3b83d8a52b57da7f035a126bf458e7322cadbc2d 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarManager.java
@@ -67,7 +67,9 @@ public class SnackbarManager implements OnClickListener, OnGlobalLayoutListener
     }
 
     /**
-     * Interface that shows the ability to provide a unified snackbar manager.
+     * Interface that shows the ability to provide a snackbar manager. Activities implementing this
+     * interface must call {@link SnackbarManager#onStart()} and {@link SnackbarManager#onStop()} in
+     * corresponding lifecycle events.
      */
     public interface SnackbarManageable {
         /**
@@ -123,6 +125,7 @@ public class SnackbarManager implements OnClickListener, OnGlobalLayoutListener
     private final Handler mUIThreadHandler;
     private Stack<Snackbar> mStack = new Stack<Snackbar>();
     private SnackbarPopupWindow mPopup;
+    private boolean mActivityInForeground;
     private final Runnable mHideRunnable = new Runnable() {
         @Override
         public void run() {
@@ -145,10 +148,27 @@ public class SnackbarManager implements OnClickListener, OnGlobalLayoutListener
     }
 
     /**
+     * Notifies the snackbar manager that the activity is running in foreground now.
+     */
+    public void onStart() {
+        mActivityInForeground = true;
+    }
+
+    /**
+     * Notifies the snackbar manager that the activity has been pushed to background.
+     */
+    public void onStop() {
+        dismissAllSnackbars(false);
+        mActivityInForeground = false;
+    }
+
+    /**
      * Shows a snackbar at the bottom of the screen, or above the keyboard if the keyboard is
      * visible.
      */
     public void showSnackbar(Snackbar snackbar) {
+        if (!mActivityInForeground) return;
+
         int durationMs = snackbar.getDuration();
         if (durationMs == 0) {
             durationMs = DeviceClassManager.isAccessibilityModeEnabled(mDecor.getContext())
@@ -185,6 +205,8 @@ public class SnackbarManager implements OnClickListener, OnGlobalLayoutListener
     public void dismissAllSnackbars(boolean isTimeout) {
         mUIThreadHandler.removeCallbacks(mHideRunnable);
 
+        if (!mActivityInForeground) return;
+
         if (mPopup != null) {
             // TODO(ianwen): remove the try catch after crbug.com/553569 is fixed.
             try {