[NoStatePrefetch] Support only GET and HEAD

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 200e2865557792db5a3c5c694c05a6bfac76474b..2ed43b81345901874916ed5fe529478dd48365f7 100644
--- a/chrome/browser/prerender/prerender_resource_throttle.cc
+++ b/chrome/browser/prerender/prerender_resource_throttle.cc
@@ -121,8 +121,13 @@ void PrerenderResourceThrottle::WillStartRequestOnUI(
   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);