Report was_cached in SubresourceLoadInfo

This change adds a boolean `was_cached` to the SubresourceLoadInfo
struct. This lets consumers know whether or not the response was
fetched from the network cache. Notably, this is important for
recording page load metrics when the Network Service is enabled.

This reverts commit 0b2b1a92.

Issues in the previous commit are fixed by retaining the exists_in_cache
field.

In a many cases when NavigationURLLoaderDelegate::OnRequestFailed() is
called, NavigationURLLoaderNetworkService::OnResponseStarted() has not
been called. In these cases, we cannot rely on using a stored
was_cached value, since it may not be properly updated.

BUG=816684,822237

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I0beb72b825ae0a12122170cec2e4f4358dda58af
Reviewed-on: https://chromium-review.googlesource.com/966792Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Jay Civelli <jcivelli@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Conley Owens <cco3@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545626}

content/browser/web_contents/web_contents_impl_browsertest.cc

@@ -594,6 +594,7 @@ IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest,
   GURL subresource_url = embedded_test_server()->GetURL("/cachetime");
   ASSERT_TRUE(subresource_load_info);
   EXPECT_EQ(subresource_url, subresource_load_info->url);
+  EXPECT_FALSE(subresource_load_info->was_cached);
   observer.Reset();
 
   // Loading again should serve the request out of the in-memory cache.
@@ -611,6 +612,7 @@ IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest,
   subresource_load_info = observer.last_subresource_load_info();
   ASSERT_TRUE(subresource_load_info);
   EXPECT_EQ(subresource_url, subresource_load_info->url);
+  EXPECT_TRUE(subresource_load_info->was_cached);
   EXPECT_FALSE(observer.last_memory_cached_loaded_url().is_valid());
 }
 

content/public/common/subresource_load_info.mojom

@@ -25,4 +25,7 @@ struct SubresourceLoadInfo {
 
   // The host IP.
   net.interfaces.IPAddress? ip;
+
+  // True if the response was fetched from the network cache.
+  bool was_cached;
 };

content/renderer/loader/resource_dispatcher.cc

@@ -273,6 +273,7 @@ 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->was_cached = status.exists_in_cache;
     NotifySubresourceLoadComplete(
         RenderThreadImpl::DeprecatedGetMainTaskRunner(),
         request_info->render_frame_id, std::move(subresource_load_info));