Add a class to replace ImageLoadingTracker with a nicer API.

chrome/browser/extensions/extension_install_prompt.h

Index: chrome/browser/extensions/extension_install_prompt.h
diff --git a/chrome/browser/extensions/extension_install_prompt.h b/chrome/browser/extensions/extension_install_prompt.h
index 1b65fa66e69dde2441baf2f9a487630102c3a587..155960ab7cae815c04d169d42e0f460f32b45eb1 100644
--- a/chrome/browser/extensions/extension_install_prompt.h
+++ b/chrome/browser/extensions/extension_install_prompt.h
@@ -12,7 +12,6 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/string16.h"
 #include "chrome/browser/extensions/crx_installer_error.h"
-#include "chrome/browser/extensions/image_loading_tracker.h"
 #include "chrome/common/extensions/url_pattern.h"
 #include "google_apis/gaia/oauth2_mint_token_flow.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ -42,8 +41,9 @@ class PermissionSet;
 }  // namespace extensions
 
 // Displays all the UI around extension installation.
-class ExtensionInstallPrompt : public ImageLoadingTracker::Observer,
-                               public OAuth2MintTokenFlow::Delegate {
+class ExtensionInstallPrompt
+    : public OAuth2MintTokenFlow::Delegate,
+      public base::SupportsWeakPtr<ExtensionInstallPrompt> {
  public:
   enum PromptType {
     UNSET_PROMPT_TYPE = -1,
@@ -240,11 +240,6 @@ class ExtensionInstallPrompt : public ImageLoadingTracker::Observer,
   // Installation failed. This is declared virtual for testing.
   virtual void OnInstallFailure(const extensions::CrxInstallerError& error);
 
-  // ImageLoadingTracker::Observer:
-  virtual void OnImageLoaded(const gfx::Image& image,
-                             const std::string& extension_id,
-                             int index) OVERRIDE;
-
  protected:
   friend class extensions::ExtensionWebstorePrivateApiTest;
   friend class WebstoreInlineInstallUnpackFailureTest;
@@ -260,6 +255,9 @@ class ExtensionInstallPrompt : public ImageLoadingTracker::Observer,
   // an empty bitmap, then a default icon will be used instead.
   void SetIcon(const SkBitmap* icon);
 
+  // extension_image_utils callback.
+  void OnImageLoaded(const gfx::Image& image);
+
   // Starts the process of showing a confirmation UI, which is split into two.
   // 1) Set off a 'load icon' task.
   // 2) Handle the load icon response and show the UI (OnImageLoaded).
@@ -307,10 +305,6 @@ class ExtensionInstallPrompt : public ImageLoadingTracker::Observer,
   PromptType prompt_type_;
 
   scoped_ptr<OAuth2MintTokenFlow> token_flow_;
-
-  // Keeps track of extension images being loaded on the File thread for the
-  // purpose of showing the install UI.
-  ImageLoadingTracker tracker_;
 };
 
 namespace chrome {