Implement ManifestFetcher, helper to fetch Web Manifests.

content/renderer/web_ui_mojo_context_state.cc

Index: content/renderer/web_ui_mojo_context_state.cc
diff --git a/content/renderer/web_ui_mojo_context_state.cc b/content/renderer/web_ui_mojo_context_state.cc
index 3c9956867ef454377d60f9195f40dbbd0d94b2d2..7757b26cf1316c0f3fcb45a32651a113cb7ee7d3 100644
--- a/content/renderer/web_ui_mojo_context_state.cc
+++ b/content/renderer/web_ui_mojo_context_state.cc
@@ -100,6 +100,7 @@ void WebUIMojoContextState::FetchModule(const std::string& id) {
   fetcher->Start(frame_,
                  blink::WebURLRequest::RequestContextScript,
                  blink::WebURLRequest::FrameTypeNone,
+                 ResourceFetcher::PLATFORM_LOADER,
                  base::Bind(&WebUIMojoContextState::OnFetchModuleComplete,
                             base::Unretained(this),
                             fetcher));