Prerender: NoStatePrefetch browser side changes.

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index 60cdd13904c785ede93b57e1245da33b285de263..d4a051baacc8b9b6d0da708076473626aaad3f9a 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -321,6 +321,10 @@ bool PrerenderManager::MaybeUsePrerenderedPage(const GURL& url,
     return false;
   DCHECK(prerender_data->contents());
 
+  if (prerender_data->contents()->prerender_mode() != FULL_PRERENDER) {
+    return false;
+  }

[mmenke, 2016/08/22 14:17:58]

nit:  Remove braces

[mattcary, 2016/08/23 10:53:56]

Done.

+
   std::unique_ptr<WebContents> new_web_contents = SwapInternal(
       url, web_contents, prerender_data, params->should_replace_current_entry);
   if (!new_web_contents)
@@ -572,6 +576,8 @@ const char* PrerenderManager::GetModeString() {
       return "_15MinTTL";
     case PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP:
       return "_NoUse";
+    case PRERENDER_MODE_NOSTATE_PREFETCH:
+      return "_NoStatePrefetch";

[mmenke, 2016/08/22 14:17:58]

Need to update histograms.xml for this addition.

[mattcary, 2016/08/23 10:53:56]

Done.

I see that the PrerenderMode histogram in histograms.xml was marked deprecated
in 16 Nov 2012. Should I un-deprecate or do anything else?

[mmenke, 2016/08/23 14:35:27]

Hrm...you're right.  I'd say no.  Looks like a lot of the prerender histograms
(Including all that use this method...) should just be removed.

     case PRERENDER_MODE_MAX:
     default:
       NOTREACHED() << "Invalid PrerenderManager mode.";
@@ -600,6 +606,11 @@ bool PrerenderManager::IsNoUseGroup() {
   return GetMode() == PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP;
 }
 
+// static
+bool PrerenderManager::IsNoStatePrefetch() {
+  return GetMode() == PRERENDER_MODE_NOSTATE_PREFETCH;
+}
+
 bool PrerenderManager::IsWebContentsPrerendering(
     const WebContents* web_contents,
     Origin* origin) const {
@@ -677,8 +688,11 @@ std::vector<WebContents*> PrerenderManager::GetAllPrerenderingContents() const {
   std::vector<WebContents*> result;
 
   for (const auto& prerender : active_prerenders_) {
-    if (WebContents* contents = prerender->contents()->prerender_contents())
+    WebContents* contents = prerender->contents()->prerender_contents();

[mmenke, 2016/08/22 14:17:58]

So we do create a WebContents in the non-full prerender case, but we don't
return it here?  Why not?

If this is important behavior, should have a test for it.

[mattcary, 2016/08/23 10:53:56]

AFAIK, we will have a WebContents for the prefetching render because we will
have a renderer process for actually loading & preload scanning the main
resource. But we never want to swap into this renderer, because no renderering
has been done.

The only non-test use of GetAllPrerenderingContents is in tab_android.cc where
by context we're only interested in prerenders that have finished loading. We
won't want a prefetching prerenderer to appear in that case so making the
semantics of GetAllPrerenderingContents return only full prerenderers seems like
the right things to do.

There is a test use of this ftn in extensions/activity_log that looks like it
will probably break when/if full prerendering is deprecated (as it expects an
omnibox-initiated prerender appear in the result of this ftn). If that happens,
though, we will probably want to remove or change all uses of this ftn anyway as
prerendering will mean something quite different from what it used to.

I looked into adding a test to prerender_unittests.cc, but
GetAllPrerenderingContents requires WebContent instances, not just
PrerenderContents, and creating one of those in a unittest context seems
impractical (I played around with WebContentsTester and TestBrowserContext, but
it appears the TestBrowserContext doesn't do enough for the TestWebContents to
init with seg faulting).

+    if (contents &&
+        prerender->contents()->prerender_mode() == FULL_PRERENDER) {
       result.push_back(contents);
+    }
   }
 
   return result;
@@ -936,6 +950,9 @@ std::unique_ptr<PrerenderHandle> PrerenderManager::AddPrerender(
       CreatePrerenderContents(url, referrer, origin);
   DCHECK(prerender_contents);
   PrerenderContents* prerender_contents_ptr = prerender_contents.get();
+  if (IsNoStatePrefetch()) {
+    prerender_contents_ptr->SetPrerenderMode(PREFETCH_ONLY);
+  }

[mmenke, 2016/08/22 14:17:58]

nit:  Remove braces

[mattcary, 2016/08/23 10:53:56]

Done.

   active_prerenders_.push_back(
       base::MakeUnique<PrerenderData>(this, std::move(prerender_contents),
                                       GetExpiryTimeForNewPrerender(origin)));