memory_coordinator: Discard tabs under critical memory condition

chrome/browser/memory/tab_manager.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 #define CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 81 matching lines @@
 
   // Returns true if |contents| is currently discarded.
   bool IsTabDiscarded(content::WebContents* contents) const;
 
   // Goes through a list of checks to see if a tab is allowed to be discarded by
   // the automatic tab discarding mechanism. Note that this is not used when
   // discarding a particular tab from about:discards.
   bool CanDiscardTab(int64_t target_web_contents_id) const;
 
   // Discards a tab to free the memory occupied by its renderer. The tab still
-  // exists in the tab-strip; clicking on it will reload it.
-  void DiscardTab();
+  // exists in the tab-strip; clicking on it will reload it. Returns true if
+  // a tab is actually discarded.

[haraken, 2017/03/07 08:04:57]

the tab was

+  bool DiscardTab();
 
   // Discards a tab with the given unique ID. The tab still exists in the
   // tab-strip; clicking on it will reload it. Returns null if the tab cannot
   // be found or cannot be discarded. Otherwise returns the new web_contents
   // of the discarded tab.
   content::WebContents* DiscardTabById(int64_t target_web_contents_id);
 
   // Method used by the extensions API to discard tabs. If |contents| is null,
   // discards the least important tab using DiscardTab(). Otherwise discards
   // the given contents. Returns the new web_contents or null if no tab
@@ skipping 312 matching lines @@
 
   // Weak pointer factory used for posting delayed tasks to task_runner_.
   base::WeakPtrFactory<TabManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TabManager);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_MANAGER_H_