Add a trace event for ResourceFetcher::requestResource

This could help better understand the Blink resource-fetching overhead
seen, for example, in XMLHttpRequest.send().

R=japhet@chromium.org
BUG=348655

Review URL: https://codereview.chromium.org/213353003

git-svn-id: svn://svn.chromium.org/blink/trunk@170676 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp

@@ -598,6 +598,8 @@ ResourcePtr<Resource> ResourceFetcher::requestResource(Resource::Type type, Fetc
 {
     ASSERT(request.options().synchronousPolicy == RequestAsynchronously || type == Resource::Raw);
 
+    TRACE_EVENT0("webkit", "ResourceFetcher::requestResource");
+
     KURL url = request.resourceRequest().url();
 
     WTF_LOG(ResourceLoading, "ResourceFetcher::requestResource '%s', charset '%s', priority=%d, forPreload=%u, type=%s", url.elidedString().latin1().data(), request.charset().latin1().data(), request.priority(), request.forPreload(), ResourceTypeName(type));