Prerender: NoStatePrefetch browser side changes.

chrome/browser/prerender/prerender_manager.cc

 // Copyright (c) 2012 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_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <functional>
@@ skipping 303 matching lines @@
   // First, try to find prerender data with the correct session storage
   // namespace.
   // TODO(ajwong): This doesn't handle isolated apps correctly.
   PrerenderData* prerender_data = FindPrerenderData(
       url,
       web_contents->GetController().GetDefaultSessionStorageNamespace());
   if (!prerender_data)
     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)
     return false;
 
   // Record the new target_contents for the callers.
   params->target_contents = new_web_contents.release();
   return true;
 }
 
@@ skipping 231 matching lines @@
     case PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP:
       return "_Enabled";
     case PRERENDER_MODE_EXPERIMENT_CONTROL_GROUP:
       return "_Control";
     case PRERENDER_MODE_EXPERIMENT_MULTI_PRERENDER_GROUP:
       return "_Multi";
     case PRERENDER_MODE_EXPERIMENT_15MIN_TTL_GROUP:
       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.";
       break;
   }
   return "";
 }
 
 // static
 bool PrerenderManager::IsPrerenderingPossible() {
   return GetMode() != PRERENDER_MODE_DISABLED;
 }
 
 // static
 bool PrerenderManager::ActuallyPrerendering() {
   return IsPrerenderingPossible() && !IsControlGroup();
 }
 
 // static
 bool PrerenderManager::IsControlGroup() {
   return GetMode() == PRERENDER_MODE_EXPERIMENT_CONTROL_GROUP;
 }
 
 // static
 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 {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   PrerenderContents* prerender_contents = GetPrerenderContents(web_contents);
   if (!prerender_contents)
     return false;
 
   if (origin)
     *origin = prerender_contents->origin();
@@ skipping 57 matching lines @@
     int route_id) const {
   WebContents* web_contents = tab_util::GetWebContentsByID(child_id, route_id);
   return web_contents ? GetPrerenderContents(web_contents) : nullptr;
 }
 
 std::vector<WebContents*> PrerenderManager::GetAllPrerenderingContents() const {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   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;
 }
 
 bool PrerenderManager::HasRecentlyBeenNavigatedTo(Origin origin,
                                                   const GURL& url) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   CleanUpOldNavigations();
@@ skipping 237 matching lines @@
     // by a navigation and is unlikely to be the same site.
     RecordFinalStatusWithoutCreatingPrerenderContents(
         url, origin, FINAL_STATUS_RATE_LIMIT_EXCEEDED);
     return nullptr;
   }
 
   std::unique_ptr<PrerenderContents> prerender_contents =
       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)));
   if (!prerender_contents_ptr->Init()) {
     DCHECK(active_prerenders_.end() ==
            FindIteratorForPrerenderContents(prerender_contents_ptr));
     return nullptr;
   }
 
   histograms_->RecordPrerenderStarted(origin);
@@ skipping 342 matching lines @@
   DCHECK_EQ(1u, erased);
 }
 
 void PrerenderManager::SetPrerenderContentsFactoryForTest(
     PrerenderContents::Factory* prerender_contents_factory) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   prerender_contents_factory_.reset(prerender_contents_factory);
 }
 
 }  // namespace prerender