[NoStatePrefetch] Support only GET and HEAD

chrome/browser/prerender/prerender_resource_throttle.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/prerender/prerender_resource_throttle.h"
 
 #include "base/logging.h"
 #include "base/numerics/safe_conversions.h"
 #include "build/build_config.h"
 #include "chrome/browser/prerender/prerender_final_status.h"
@@ skipping 103 matching lines @@
     ResourceType resource_type,
     int render_process_id,
     int render_frame_id,
     const GURL& url) {
   bool cancel = false;
   PrerenderContents* prerender_contents =
       PrerenderContentsFromRenderFrame(render_process_id, render_frame_id);
   if (prerender_contents) {
     // Abort any prerenders that spawn requests that use unsupported HTTP
     // methods or schemes.
-    if (!PrerenderManager::IsValidHttpMethod(method)) {
-      prerender_contents->Destroy(FINAL_STATUS_INVALID_HTTP_METHOD);
+    if (!prerender_contents->IsValidHttpMethod(method)) {
+      // If the HTTP method is invalid, cancel the request, but don't cancel the
+      // whole prefetch unless this is the main frame.

[mmenke, 2016/09/21 16:56:20]

Think this would be clearer if it said what we're doing here, not what we're not
doing here.

i.e., something like:  "If this is a full prerender, cancel the prerender in
response to invalid requests.  For prefetches, cancel invalid requests but keep
the prerender going, unless it's the main frame that's invalid."

I'm also fine with removing the main frame check, if you want - if it's an
invalid URL, we'll just pass the ERR_ABORTED on to the renderer, anyways, when
we cancel the request, so not like anything particularly exciting will happen if
we don't cancel the prerender.  Up to you, I'm good, either way.

[droger, 2016/09/22 08:42:01]

Done.

+      if (prerender_contents->prerender_mode() == FULL_PRERENDER ||
+          resource_type == content::RESOURCE_TYPE_MAIN_FRAME) {
+        prerender_contents->Destroy(FINAL_STATUS_INVALID_HTTP_METHOD);
+      }
       cancel = true;
     } else if (!PrerenderManager::DoesSubresourceURLHaveValidScheme(url)) {
       prerender_contents->Destroy(FINAL_STATUS_UNSUPPORTED_SCHEME);
       ReportUnsupportedPrerenderScheme(url);
       cancel = true;
 #if defined(OS_ANDROID)
     } else if (resource_type == content::RESOURCE_TYPE_FAVICON) {
       // Delay icon fetching until the contents are getting swapped in
       // to conserve network usage in mobile devices.
       prerender_contents->AddResourceThrottle(throttle);
@@ skipping 83 matching lines @@
   if (g_prerender_contents_for_testing)
     return g_prerender_contents_for_testing;
   content::RenderFrameHost* rfh = content::RenderFrameHost::FromID(
       render_process_id, render_frame_id);
   content::WebContents* web_contents =
       content::WebContents::FromRenderFrameHost(rfh);
   return PrerenderContents::FromWebContents(web_contents);
 }
 
 }  // namespace prerender