Make DisplayInfoProvider an interface

chrome/browser/extensions/api/system_display/display_info_provider.h

 // Copyright 2013 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_EXTENSIONS_API_SYSTEM_DISPLAY_DISPLAY_INFO_PROVIDER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_DISPLAY_DISPLAY_INFO_PROVIDER_H_
 
 #include <string>
 #include <vector>
 
-#include "chrome/common/extensions/api/system_display.h"
+#include "base/macros.h"
+#include "base/memory/linked_ptr.h"
 
 namespace gfx {
 class Display;
 }
 
 namespace extensions {
 
-typedef std::vector<linked_ptr<
-    api::system_display::DisplayUnitInfo> > DisplayInfo;
+namespace api {
+namespace system_display {
+struct DisplayProperties;
+struct DisplayUnitInfo;
+}
+}
+
+typedef std::vector<linked_ptr<api::system_display::DisplayUnitInfo> >
+    DisplayInfo;
 
 class DisplayInfoProvider {
- public :
+ public:
+  virtual ~DisplayInfoProvider();
+
+  // Returns a pointer to DisplayInfoProvider or NULL if Create()
+  // or InitializeForTesting() or not called yet.
   static DisplayInfoProvider* Get();
 
-  DisplayInfoProvider();
-  virtual ~DisplayInfoProvider();
-
   // This is for tests that run in its own process (e.g. browser_tests).
   // Using this in other tests (e.g. unit_tests) will result in DCHECK failure.
   static void InitializeForTesting(DisplayInfoProvider* display_info_provider);
 
+  // Updates the display with |display_id| according to |info|. Returns whether
+  // the display was successfully updated. On failure, no display parameters
+  // should be changed, and |error| should be set to the error string.
+  virtual bool SetInfo(const std::string& display_id,
+                       const api::system_display::DisplayProperties& info,
+                       std::string* error) = 0;
+
   DisplayInfo GetAllDisplaysInfo();
 
-  virtual bool SetInfo(const std::string& display_id,
-                       const api::system_display::DisplayProperties& info,
-                       std::string* error);
+ protected:
+  DisplayInfoProvider();
 
  private:
+  static DisplayInfoProvider* Create();
+
   // Update the content of the |unit| obtained for |display| using
   // platform specific method.
   virtual void UpdateDisplayUnitInfoForPlatform(
       const gfx::Display& display,
-      extensions::api::system_display::DisplayUnitInfo* unit);
+      api::system_display::DisplayUnitInfo* unit) = 0;
 
   DISALLOW_COPY_AND_ASSIGN(DisplayInfoProvider);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_SYSTEM_DISPLAY_DISPLAY_INFO_PROVIDER_H_