Add option to disallow the discarding of a tab that was previously discarded.

chrome/browser/ui/tabs/tab_discard_state.h

Index: chrome/browser/ui/tabs/tab_discard_state.h
diff --git a/chrome/browser/ui/tabs/tab_discard_state.h b/chrome/browser/ui/tabs/tab_discard_state.h
new file mode 100644
index 0000000000000000000000000000000000000000..5bdd203f18cba30850b070f8cbafa12d5a4158af
--- /dev/null
+++ b/chrome/browser/ui/tabs/tab_discard_state.h
@@ -0,0 +1,52 @@
+// Copyright 2015 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_UI_TABS_TAB_DISCARD_STATE_H_
+#define CHROME_BROWSER_UI_TABS_TAB_DISCARD_STATE_H_
+
+#include "base/supports_user_data.h"
+
+namespace content {
+class WebContents;
+}
+
+// Manages the information about the discarding state of a tab. This data is
+// stored in WebContents.
+class TabDiscardState : public base::SupportsUserData::Data {
+ public:
+  // Returns the TabDiscardState associated with |web_contents|. It will create
+  // one if none exists.
+  static TabDiscardState* Get(content::WebContents* web_contents);
+
+  // Sets the TabDiscardState of a |web_contents|. The object referenced by
+  // |state| is now owned by |web_contents|
+  static void Set(content::WebContents* web_contents, TabDiscardState* state);
+
+  // Returns true if |web_contents| has been discarded to save memory.
+  static bool IsDiscarded(content::WebContents* web_contents);
+
+  // Sets/clears the discard state of |web_contents|.
+  static void SetDiscardState(content::WebContents* web_contents, bool state);
+
+  // Returns the number of times |web_contents| has been discarded.
+  static int DiscardCount(content::WebContents* web_contents);
+
+  // Increments the number of times |web_contents| has been discarded.
+  static void IncrementDiscardCount(content::WebContents* web_contents);
+
+  // Copies the discard state from |old_contents| to |new_contents|.
+  static void CopyState(content::WebContents* old_contents,
+                        content::WebContents* new_contents);
+
+  TabDiscardState() : is_discarded_(false), discard_count_(0) {}
+
+ private:
+  // Is the tab currently discarded?
+  bool is_discarded_;
+
+  // Number of times the tab has been discarded.
+  int discard_count_;
+};
+
+#endif  // CHROME_BROWSER_UI_TABS_TAB_DISCARD_STATE_H_