Add signals to make callback more reliable

chrome/android/java/src/android/support/customtabs/CustomTabsCallback.java

Index: chrome/android/java/src/android/support/customtabs/CustomTabsCallback.java
diff --git a/chrome/android/java/src/android/support/customtabs/CustomTabsCallback.java b/chrome/android/java/src/android/support/customtabs/CustomTabsCallback.java
index 899556c2054c4a486444fd5a3c84c8f76180a6e1..135aa0970ad207d4afc51a2a9d53752a463d8487 100644
--- a/chrome/android/java/src/android/support/customtabs/CustomTabsCallback.java
+++ b/chrome/android/java/src/android/support/customtabs/CustomTabsCallback.java
@@ -21,6 +21,27 @@ public class CustomTabsCallback {
     public static final int NAVIGATION_FINISHED = 2;
 
     /**
+     * Sent when the tab couldn't finish loading due to a failure.
+     */
+    public static final int NAVIGATION_FAILED = 3;
+
+    /**
+     * Sent when loading was aborted by a user action before it finishes like clicking on a link
+     * or refreshing the page.
+     */
+    public static final int NAVIGATION_ABORTED = 4;
+
+    /**
+     * Sent when the tab becomes visible.
+     */
+    public static final int TAB_SHOWN = 5;
+
+    /**
+     * Sent when the tab becomes hidden.
+     */
+    public static final int TAB_HIDDEN = 6;
+
+    /**
      * To be called when a navigation event happens.
      *
      * @param navigationEvent The code corresponding to the navigation event.