[NoStatePrefetch] Add UMA histogram to count prefetch requests

chrome/browser/prerender/prerender_resource_throttle.cc

Index: chrome/browser/prerender/prerender_resource_throttle.cc
diff --git a/chrome/browser/prerender/prerender_resource_throttle.cc b/chrome/browser/prerender/prerender_resource_throttle.cc
index a23b5a9336e5327187b117b1c04e2ecb1fab6804..3feefa422af01bf6a7838255fc5b23e3909ae857 100644
--- a/chrome/browser/prerender/prerender_resource_throttle.cc
+++ b/chrome/browser/prerender/prerender_resource_throttle.cc
@@ -13,6 +13,7 @@
 #include "content/public/browser/resource_controller.h"
 #include "content/public/browser/resource_request_info.h"
 #include "content/public/browser/web_contents.h"
+#include "net/http/http_response_headers.h"
 #include "net/url_request/redirect_info.h"
 #include "net/url_request/url_request.h"
 
@@ -25,7 +26,7 @@ static const char kFollowOnlyWhenPrerenderShown[] =
     "follow-only-when-prerender-shown";
 
 PrerenderContents* g_prerender_contents_for_testing;
-}
+}  // namespace
 
 void PrerenderResourceThrottle::OverridePrerenderContentsForTesting(
     PrerenderContents* contents) {
@@ -67,6 +68,28 @@ void PrerenderResourceThrottle::WillRedirectRequest(
                  redirect_info.new_url));
 }
 
+void PrerenderResourceThrottle::WillProcessResponse(bool* defer) {

[pasko, 2016/08/30 13:41:04]

is it possible to detect redirects on the path to main resource here? If yes,
then we could make more buckets: "MAIN_RESOURCE_REDIRECTS_ALL_CACHEABLE",
"MAIN_RESOURCE_REDIRECTS_SOME_NO_STORE"

TODO for later would SG to me as well

[droger, 2016/08/30 14:31:41]

Good idea.

We can detect redirects easily, and reporting each redirect should be easy.

Reporting info regarding the whole redirect chain may be harder but probably
doable too. However, this would probably be in a separate histogram in this
case? I'll do this in a separate CL because it may not be trivial.

+  *defer = false;

[pasko, 2016/08/30 13:41:04]

I am not familiar with resource throttle API, of course, but ..

other implementations of WillProcessResponse seem to mostly avoid touching the
output argument on early return (such as when ResourceRequestInfo not
available). Seems safer in various edge cases when info is not available during
hypothetical shutdown and the space for |defer| is already gone.

[droger, 2016/08/30 14:31:41]

Done.

I wondered about this, and both cases definitely exist in the codebase. I don't
have a strong preference.

+
+  const content::ResourceRequestInfo* info =
+      content::ResourceRequestInfo::ForRequest(request_);
+  if (!info)
+    return;
+
+  bool is_no_store = false;
+  const net::HttpResponseInfo& response_info = request_->response_info();
+  if (response_info.headers.get()) {
+    is_no_store =
+        response_info.headers->HasHeaderValue("cache-control", "no-store");
+  }
+
+  content::BrowserThread::PostTask(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(&PrerenderResourceThrottle::WillProcessResponseOnUI,
+                 content::IsResourceTypeFrame(info->GetResourceType()),
+                 is_no_store, info->GetChildID(), info->GetRenderFrameID()));
+}
+
 const char* PrerenderResourceThrottle::GetNameForLogging() const {
   return "PrerenderResourceThrottle";
 }
@@ -79,6 +102,7 @@ void PrerenderResourceThrottle::Cancel() {
   controller()->Cancel();
 }
 
+// static
 void PrerenderResourceThrottle::WillStartRequestOnUI(
     const base::WeakPtr<PrerenderResourceThrottle>& throttle,
     const std::string& method,
@@ -116,6 +140,7 @@ void PrerenderResourceThrottle::WillStartRequestOnUI(
                  &PrerenderResourceThrottle::Resume, throttle));
 }
 
+// static
 void PrerenderResourceThrottle::WillRedirectRequestOnUI(
     const base::WeakPtr<PrerenderResourceThrottle>& throttle,
     const std::string& follow_only_when_prerender_shown_header,
@@ -157,6 +182,24 @@ void PrerenderResourceThrottle::WillRedirectRequestOnUI(
                  &PrerenderResourceThrottle::Resume, throttle));
 }
 
+// static
+void PrerenderResourceThrottle::WillProcessResponseOnUI(bool is_main_resource,
+                                                        bool is_no_store,
+                                                        int render_process_id,
+                                                        int render_frame_id) {
+  PrerenderContents* prerender_contents =

[pasko, 2016/08/30 13:41:05]

nit: DCHECK_CURRENTLY_ON

+      PrerenderContentsFromRenderFrame(render_process_id, render_frame_id);
+  if (!prerender_contents)
+    return;
+
+  if (prerender_contents->prerender_mode() != PREFETCH_ONLY)
+    return;
+
+  prerender_contents->prerender_manager()->RecordResourcePrefetch(
+      prerender_contents->origin(), is_main_resource, is_no_store);
+}
+
+// static
 PrerenderContents* PrerenderResourceThrottle::PrerenderContentsFromRenderFrame(
     int render_process_id, int render_frame_id) {
   if (g_prerender_contents_for_testing)