Copy previews state to net::ResourceRequest from common params

PreviewsState is used in DataReductionProxyURLLoaderThrottle to set some
chrome-proxy specific headers to serve previews.

Bug: 893728
Change-Id: Ie54f174bb1ba2ff4d77f725c0e64450f8d2aad0c
Reviewed-on: https://chromium-review.googlesource.com/c/1327568Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: rajendrant <rajendrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606661}

content/browser/loader/navigation_url_loader_impl.cc

@@ -267,6 +267,7 @@ std::unique_ptr<network::ResourceRequest> CreateResourceRequest(
   new_request->upgrade_if_insecure = request_info->upgrade_if_insecure;
   new_request->throttling_profile_id = request_info->devtools_frame_token;
   new_request->transition_type = request_info->common_params.transition;
+  new_request->previews_state = request_info->common_params.previews_state;
   return new_request;
 }