S13nServiceWorker: Pass SharedWorkerServiceImplTest

When S13nServiceWorker is enabled these tests requre an instance
of URLLoaderFactory. Add a mock URLLoaderFactory and set them in
tests. This makes tests pass.

Bug: 860361
Change-Id: I2cfa371c1c1076d895398686b3df36340664e30b
Reviewed-on: https://chromium-review.googlesource.com/1152337Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579243}

content/public/test/mock_render_process_host.cc

@@ -57,6 +57,7 @@ MockRenderProcessHost::MockRenderProcessHost(BrowserContext* browser_context)
       child_identity_(mojom::kRendererServiceName,
                       BrowserContext::GetServiceUserIdFor(browser_context),
                       base::StringPrintf("%d", id_)),
+      url_loader_factory_(nullptr),
       weak_ptr_factory_(this) {
   // Child process security operations can't be unit tested unless we add
   // ourselves as an existing child process.