Headless: Add GenericURLRequestJob::IsBrowserSideFetch

This lets a C++ embedder tell if a request was sent from the browser
or the renderer.

Bug: 
Change-Id: Id191dbc3003facc5125b17f38922b4d59ed67811
Reviewed-on: https://chromium-review.googlesource.com/746646Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512833}

headless/public/util/generic_url_request_job.cc

@@ -299,6 +299,12 @@ bool GenericURLRequestJob::IsAsync() const {
   return true;
 }
 
+bool GenericURLRequestJob::IsBrowserSideFetch() const {
+  if (!request_resource_info_)
+    return false;
+  return request_resource_info_->GetFrameTreeNodeId() != -1;
+}
+
 namespace {
 void CompletionCallback(int* dest, base::Closure* quit_closure, int value) {
   *dest = value;

headless/public/util/generic_url_request_job.h

@@ -56,6 +56,9 @@ class HEADLESS_EXPORT Request {
   // Returns the size of the POST data, if any, from the net::URLRequest.
   virtual uint64_t GetPostDataSize() const = 0;
 
+  // Returns true if the fetch was issues by the browser.
+  virtual bool IsBrowserSideFetch() const = 0;
+
   enum class ResourceType {
     MAIN_FRAME = 0,
     SUB_FRAME = 1,
@@ -159,6 +162,7 @@ class HEADLESS_EXPORT GenericURLRequestJob
   uint64_t GetPostDataSize() const override;
   ResourceType GetResourceType() const override;
   bool IsAsync() const override;
+  bool IsBrowserSideFetch() const override;
 
  private:
   void PrepareCookies(const GURL& rewritten_url,