Fix three crashes in the recent tabs dialog.

This fixes a crash in the recent tabs dialog when clicking on a recently
closed tab and clicking the dialog's "X" button almost simultaneously.

The crash happened because when "X" is clicked, the dialog would be
dismissed and the RecentTabsPage would be destroyed. Soon thereafter,
the click on the recently closed item would be processed and it would
try to use the RecentTabsPage object.

This CL fixes the crash by tracking whether the RecentTabsManager has
been destroyed and ignoring clicks that happen after destroy has been
called. This also fixes an identical crash with clicking a foreign
session tab, and a related (but rarer) crash where sync or sign-in
related events were being processed after the RecentTabsManager was
destroyed.

BUG=567891

Review URL: https://codereview.chromium.org/1521553004

Cr-Commit-Position: refs/heads/master@{#365075}
(cherry picked from commit 7f87dbd)

Review URL: https://codereview.chromium.org/1530473002 .

Cr-Commit-Position: refs/branch-heads/2564@{crosswalk-project#352}
Cr-Branched-From: 1283eca-refs/heads/master@{#359700}

chrome/android/java/src/org/chromium/chrome/browser/ntp/DocumentRecentTabsManager.java

@@ -116,6 +116,7 @@ public void openForeignSessionTab(final ForeignSession session, final ForeignSes
         ThreadUtils.postOnUiThreadDelayed(new Runnable() {
             @Override
             public void run() {
+                if (isDestroyed()) return;
                 DocumentRecentTabsManager.super.openForeignSessionTab(
                         session, tab, WindowOpenDisposition.NEW_FOREGROUND_TAB);
                 if (mDialog != null) mDialog.dismiss();
@@ -131,6 +132,7 @@ public void openRecentlyClosedTab(final RecentlyClosedTab tab, int windowDisposi
         ThreadUtils.postOnUiThreadDelayed(new Runnable() {
             @Override
             public void run() {
+                if (isDestroyed()) return;
                 DocumentRecentTabsManager.super.openRecentlyClosedTab(
                         tab, WindowOpenDisposition.NEW_FOREGROUND_TAB);
                 if (mDialog != null) mDialog.dismiss();

chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsManager.java

@@ -67,6 +67,7 @@ interface UpdatedCallback {
     private SigninManager mSignInManager;
     private UpdatedCallback mUpdatedCallback;
     private ProfileDataCache mProfileDataCache;
+    private boolean mIsDestroyed;
 
     /**
      * Create an RecentTabsManager to be used with RecentTabsPage and RecentTabsRowAdapter.
@@ -98,6 +99,7 @@ public RecentTabsManager(Tab tab, Profile profile, Context context) {
      * Should be called when this object is no longer needed. Performs necessary listener tear down.
      */
     public void destroy() {
+        mIsDestroyed = true;
         AndroidSyncSettings.unregisterObserver(mContext, this);
 
         mSignInManager.removeSignInStateObserver(this);
@@ -125,6 +127,13 @@ public void destroy() {
         InvalidationController.get(mContext).onRecentTabsPageClosed();
     }
 
+    /**
+     * Returns true if destroy() has been called.
+     */
+    public boolean isDestroyed() {
+        return mIsDestroyed;
+    }
+
     private static ForeignSessionHelper buildForeignSessionHelper(Profile profile) {
         return new ForeignSessionHelper(profile);
     }
@@ -420,6 +429,7 @@ public void androidSyncSettingsChanged() {
         ThreadUtils.runOnUiThread(new Runnable() {
             @Override
             public void run() {
+                if (mIsDestroyed) return;
                 updateForeignSessions();
                 postUpdate();
                 for (AndroidSyncSettingsObserver observer : mObservers) {