Make DisplayInfoProvider an interface

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

Index: chrome/browser/extensions/api/system_display/display_info_provider.h
diff --git a/chrome/browser/extensions/api/system_display/display_info_provider.h b/chrome/browser/extensions/api/system_display/display_info_provider.h
index 50eec2e0d1484401959ee65922f0fbdbbac4f27c..bf578de590a10405aa8e2434416adb7f5b3fd7ed 100644
--- a/chrome/browser/extensions/api/system_display/display_info_provider.h
+++ b/chrome/browser/extensions/api/system_display/display_info_provider.h
@@ -8,7 +8,8 @@
 #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;
@@ -16,32 +17,48 @@ class Display;
 
 namespace extensions {
 
-typedef std::vector<linked_ptr<
-    api::system_display::DisplayUnitInfo> > DisplayInfo;
+namespace api {
+namespace system_display {
+struct DisplayProperties;
+struct DisplayUnitInfo;
+}
+}
 
-class DisplayInfoProvider {
- public :
-  static DisplayInfoProvider* Get();
+typedef std::vector<linked_ptr<api::system_display::DisplayUnitInfo> >
+    DisplayInfo;
 
-  DisplayInfoProvider();
+class DisplayInfoProvider {
+ public:
   virtual ~DisplayInfoProvider();
 
+  // Returns a pointer to DisplayInfoProvider or NULL if Create()
+  // or InitializeForTesting() or not called yet.

[James Cook, 2014/08/19 21:48:51]

This isn't true -- it creates a new one if it doesn't exist already. Either you
should require other parts of Chrome to call Create() first (I would be OK with
that) or fix the comment.

+  static DisplayInfoProvider* Get();
+
   // 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);
 
-  DisplayInfo GetAllDisplaysInfo();
-
+  // 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);
+                       std::string* error) = 0;
+
+  DisplayInfo GetAllDisplaysInfo();
+
+ 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);
 };