[PlzNavigate] Add load flags for prefetch navigations

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 dbc6c6559b2c8986d37c1ecbba0bc76a9d3f3416..63277c9735f5362a59491ca5097a72169a9afdad 100644
--- a/chrome/browser/prerender/prerender_resource_throttle.cc
+++ b/chrome/browser/prerender/prerender_resource_throttle.cc
@@ -9,10 +9,10 @@
 #include "base/numerics/safe_conversions.h"
 #include "build/build_config.h"
 #include "chrome/browser/prerender/prerender_final_status.h"
-#include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/prerender/prerender_util.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
+#include "net/base/load_flags.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/redirect_info.h"
 #include "net/url_request/url_request.h"
@@ -83,6 +83,7 @@ void PrerenderResourceThrottle::OverridePrerenderContentsForTesting(
 
 PrerenderResourceThrottle::PrerenderResourceThrottle(net::URLRequest* request)
     : request_(request),
+      prerender_mode_(NO_PRERENDER),
       prerender_throttle_info_(new PrerenderThrottleInfo()) {}
 
 PrerenderResourceThrottle::~PrerenderResourceThrottle() {}
@@ -139,6 +140,8 @@ const char* PrerenderResourceThrottle::GetNameForLogging() const {
 }
 
 void PrerenderResourceThrottle::ResumeHandler() {
+  if (prerender_mode_ == PREFETCH_ONLY)

[mattcary, 2016/12/15 15:58:41]

Is there any reason to defer setting the load flags until Resume() happens?

It seems like there would be less chance for future inconsistency if
set_prerender_mode fiddles the load flags appropriately rather than splitting it
into two steps (set throttle prerender mode, then somewhat later setting the
load flags).

It doesn't really change anything as all the same thread hopping has to occur.

[droger, 2016/12/15 16:32:36]

Done.

+    request_->SetLoadFlags(request_->load_flags() | net::LOAD_PREFETCH);
   Resume();
 }
 
@@ -158,6 +161,10 @@ void PrerenderResourceThrottle::WillStartRequestOnUI(
     prerender_throttle_info->Set(prerender_contents->prerender_mode(),
                                  prerender_contents->origin(),
                                  prerender_contents->prerender_manager());
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&PrerenderResourceThrottle::set_prerender_mode, throttle,
+                   prerender_contents->prerender_mode()));
 
     // Abort any prerenders that spawn requests that use unsupported HTTP
     // methods or schemes.