Supply default icon to extension icon image.

chrome/browser/extensions/extension_icon_image.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_EXTENSIONS_EXTENSION_ICON_IMAGE_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_ICON_IMAGE_H_
 
 #include <map>
 #include <string>
 
@@ skipping 13 matching lines @@
 }
 
 namespace extensions {
 
 // A class that provides an ImageSkia for UI code to use. It handles extension
 // icon resource loading, screen scale factor change etc. UI code that uses
 // extension icon should host this class and be its observer. ExtensionIconImage
 // should be outlived by the observer. In painting code, UI code paints with the
 // ImageSkia provided by this class. If required extension icon resource is not
 // present, this class uses ImageLoadingTracker to load it and call on its
-// observer interface when the resource is loaded.
+// observer interface when the resource is loaded. Until the resource is loaded,
+// the UI code will be provided with blank, transparent image representation.

[Jeffrey Yasskin, 2012/08/31 18:43:14]

Do we want to return a blank image or the default image for not-yet-loaded
icons?

[tbarzic, 2012/08/31 22:29:44]

blank image.. Aaron had some concerns that returning default image here and than
soon after the loaded image could cause some weird flickering..

+// UI code can supply default icon whose representations will be added to the

[Jeffrey Yasskin, 2012/08/31 18:43:14]

By "can supply", you mean |default_icon| can be empty?

[Jeffrey Yasskin, 2012/08/31 18:43:14]

I think this comment could use a more detailed description of exactly how
representations are picked for IconImages given a set of images supplied by an
extension, including during the delay while an image is loading.

[tbarzic, 2012/08/31 22:29:44]

yeah, and in that case, if image rep is not loaded successfully nothing will be
painted.

[tbarzic, 2012/08/31 22:29:44]

ok, I've rewritten larger part of the comment, and also added a more detailed
implementation description in .cc

+// icon if a representation for some scale factor cannot be loaded from the
+// extension.
+// If default icon is supplied, it is assumed that it contains representations

[Jeffrey Yasskin, 2012/08/31 18:43:14]

By "contains representations", do you mean that, for all platform
|scale_factor|s, HasRepresentation(scale_factor) returns true, or
GetRepresentation(scale_factor) returns an ImageSkiaRep with that scale factor?

[tbarzic, 2012/08/31 22:29:44]

the latter, clarified the comment..

+// for all the scale factors supported by the current platform (e.g. MacOS).
 class IconImage : public ImageLoadingTracker::Observer,
                   public content::NotificationObserver {
  public:
   class Observer {
    public:
     // Invoked when a new image rep for an additional scale factor
     // is loaded and added to |image|.
     virtual void OnExtensionIconImageChanged(IconImage* image) = 0;
 
-    // Invoked when the icon image couldn't be loaded.
-    virtual void OnIconImageLoadFailed(IconImage* image,
-                                       ui::ScaleFactor scale_factor) = 0;
-
    protected:
     virtual ~Observer() {}
   };
 
   IconImage(const Extension* extension,
             const ExtensionIconSet& icon_set,
             int resource_size_in_dip,
+            const gfx::ImageSkia& default_icon,
             Observer* observer);
   virtual ~IconImage();
 
   const gfx::ImageSkia& image_skia() const { return image_skia_; }
 
  private:
   class Source;
 
-  typedef std::map<int, ui::ScaleFactor> LoadMap;
+  struct LoadRequest {
+    ui::ScaleFactor scale_factor;
+    bool is_async;
+  };
+
+  typedef std::map<int, LoadRequest> LoadMap;
 
   // Loads bitmap for additional scale factor.

[Jeffrey Yasskin, 2012/08/31 18:43:14]

Please describe the meaning of the return value and how the asynchronous request
is handled.

[tbarzic, 2012/08/31 22:29:44]

Done.

-  void LoadImageForScaleFactor(ui::ScaleFactor scale_factor);
+  gfx::ImageSkiaRep LoadImageForScaleFactor(ui::ScaleFactor scale_factor);
 
   // ImageLoadingTracker::Observer overrides:
   virtual void OnImageLoaded(const gfx::Image& image,
                              const std::string& extension_id,
                              int index) OVERRIDE;
 
   // content::NotificationObserver overrides:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   const Extension* extension_;
   const ExtensionIconSet& icon_set_;
   const int resource_size_in_dip_;
-  const gfx::Size desired_size_in_dip_;
 
   Observer* observer_;
 
   Source* source_;  // Owned by ImageSkia storage.
   gfx::ImageSkia image_skia_;
+  // The icon with whose representation |image_skia_| should be updated if
+  // its own representation load fails.
+  gfx::ImageSkia default_icon_;
 
   ImageLoadingTracker tracker_;
   content::NotificationRegistrar registrar_;
 
   LoadMap load_map_;
 
   DISALLOW_COPY_AND_ASSIGN(IconImage);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_ICON_IMAGE_H_