[TabManager] fixing comment at DiscardTabById function.

chrome/browser/memory/tab_manager.h

Index: chrome/browser/memory/tab_manager.h
diff --git a/chrome/browser/memory/tab_manager.h b/chrome/browser/memory/tab_manager.h
index c3f4a57f9cb4f3debb746dac4c70d01df048bdd9..0804ec0cf4043856c1bd89ef57ccabd130d9fe74 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -101,8 +101,8 @@ class TabManager : public TabStripModelObserver {
   void DiscardTab();
 
   // Discards a tab with the given unique ID. The tab still exists in the
-  // tab-strip; clicking on it will reload it. Returns true if it successfully
-  // found a tab and discarded it.
+  // tab-strip; clicking on it will reload it. Returns nullptr if it didn't find
+  // the tab or it can't be discared. Otherwise return a web_contents.

[Anderson Silva, 2016/06/08 15:57:48]

In the implementation, the returned web_contens is named null_contents. What
does it actually holds? Just some info in the TabStrip? Maybe we can put this
info here in the comment.

[Georges Khalil, 2016/06/09 13:50:52]

Let's go with this:
Returns null if the tab cannot be found or cannot be discarded. Otherwise
returns the old web_contents that got discarded. This value is mostly useful
during testing.

   content::WebContents* DiscardTabById(int64_t target_web_contents_id);
 
   // Log memory statistics for the running processes, then discards a tab.