Add signals to make callback more reliable

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
index 3e426661990a58e7c9365e74507822700eecacde..94964759984c6cef110b5944d8c3006b1d001cbf 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java
@@ -7,6 +7,7 @@ package org.chromium.chrome.browser.customtabs;
 import android.content.Intent;
 import android.net.Uri;
 import android.os.IBinder;
+import android.support.customtabs.CustomTabsCallback;
 import android.support.customtabs.CustomTabsIntent;
 import android.text.TextUtils;
 import android.view.MenuItem;
@@ -223,6 +224,14 @@ public class CustomTabActivity extends ChromeActivity {
         }
     }
 
+
+    @Override
+    public void onPauseWithNative() {
+        super.onPauseWithNative();
+        CustomTabsConnection.getInstance(getApplication()).notifyNavigationEvent(
+                mSession, CustomTabsCallback.TAB_HIDDEN);
+    }
+
     @Override
     public void onStopWithNative() {
         super.onStopWithNative();