Implement DownloadImage directly in WebStateImpl

ios/web/web_state/web_state_impl.h

Index: ios/web/web_state/web_state_impl.h
diff --git a/ios/web/web_state/web_state_impl.h b/ios/web/web_state/web_state_impl.h
index d75eb41e4ad083160e82e18bb5e2cb0b2d43fe28..5f01b93dfb94348bd19014b9d5001b7a83719afa 100644
--- a/ios/web/web_state/web_state_impl.h
+++ b/ios/web/web_state/web_state_impl.h
@@ -43,6 +43,7 @@ struct Credential;
 struct FaviconURL;
 struct LoadCommittedDetails;
 class NavigationManager;
+class ImageDataFetcher;
 class WebInterstitialImpl;
 class WebStateDelegate;
 class WebStateFacadeDelegate;
@@ -369,6 +370,9 @@ class WebStateImpl : public WebState, public NavigationManagerDelegate {
   // Mojo interface registry for this WebState.
   std::unique_ptr<service_manager::InterfaceRegistry> mojo_interface_registry_;
 
+  // Image Fetcher used to images.
+  std::unique_ptr<ImageDataFetcher> image_fetcher_;
+
   DISALLOW_COPY_AND_ASSIGN(WebStateImpl);
 };