Report mime_type in SubresourceLoadInfo

This change adds a string `mime_type` to the list of fields in
SubresourceLoadInfo.  Notably, this is important for recording page
load metrics when the Network Service is enabled.

BUG=816684

Change-Id: Ie95bd46074f2a0f915eb8378800afa0f5ed46ecd
Reviewed-on: https://chromium-review.googlesource.com/963312Reviewed-by: Jay Civelli <jcivelli@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Conley Owens <cco3@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545877}

content/browser/web_contents/web_contents_impl_browsertest.cc

@@ -575,6 +575,7 @@ IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest, SubresourceLoadComplete) {
   EXPECT_EQ(page_url, subresource_load_info->referrer);
   EXPECT_EQ("GET", subresource_load_info->method);
   EXPECT_EQ(content::RESOURCE_TYPE_IMAGE, subresource_load_info->resource_type);
+  EXPECT_EQ("image/jpeg", subresource_load_info->mime_type);
   ASSERT_TRUE(subresource_load_info->ip);
   EXPECT_EQ("127.0.0.1", subresource_load_info->ip->ToString());
 }

content/public/common/subresource_load_info.mojom

@@ -23,6 +23,9 @@ struct SubresourceLoadInfo {
   // The resource type.
   ResourceType resource_type;
 
+  // The mime type.
+  string mime_type;
+
   // The host IP.
   net.interfaces.IPAddress? ip;
 

content/renderer/loader/resource_dispatcher.cc

@@ -178,6 +178,7 @@ void ResourceDispatcher::OnReceivedResponse(
   }
 
   if (!IsResourceTypeFrame(request_info->resource_type)) {
+    request_info->mime_type = response_head.mime_type;
     NotifySubresourceStarted(RenderThreadImpl::DeprecatedGetMainTaskRunner(),
                              request_info->render_frame_id,
                              request_info->response_url,
@@ -273,6 +274,7 @@ void ResourceDispatcher::OnRequestComplete(
     subresource_load_info->resource_type = request_info->resource_type;
     if (request_info->parsed_ip.IsValid())
       subresource_load_info->ip = request_info->parsed_ip;
+    subresource_load_info->mime_type = request_info->mime_type;
     subresource_load_info->was_cached = status.exists_in_cache;
     NotifySubresourceLoadComplete(
         RenderThreadImpl::DeprecatedGetMainTaskRunner(),

content/renderer/loader/resource_dispatcher.h

@@ -192,6 +192,7 @@ class CONTENT_EXPORT ResourceDispatcher {
     linked_ptr<base::SharedMemory> buffer;
     int buffer_size;
     net::IPAddress parsed_ip;
+    std::string mime_type;
 
     // For mojo loading.
     std::unique_ptr<ThrottlingURLLoader> url_loader;