Use a precise target type for Beacon requests.

To allow the embedder to distinguish POST requests emanating from
sendBeacon() from those from a <a ping>, assign a more precise target
type to the former.

This is done in preparation for adding Beacon-Age: headers to Beacon
requests.

R=mkwst@chromium.org
BUG=398167

Review URL: https://codereview.chromium.org/468853002

git-svn-id: svn://svn.chromium.org/blink/trunk@180179 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/loader/BeaconLoader.cpp

@@ -21,8 +21,7 @@ namespace blink {
 
 void BeaconLoader::prepareRequest(LocalFrame* frame, ResourceRequest& request)
 {
-    // NOTE: do not distinguish Beacon by target type.
-    request.setRequestContext(blink::WebURLRequest::RequestContextPing);
+    request.setRequestContext(WebURLRequest::RequestContextBeacon);
     request.setHTTPMethod("POST");
     request.setHTTPHeaderField("Cache-Control", "max-age=0");
     request.setAllowStoredCredentials(true);