PlzNavigate: implement REUSE_COMMITTED_OR_PENDING_SITE for redirects

content/browser/frame_host/navigation_request.cc

Index: content/browser/frame_host/navigation_request.cc
diff --git a/content/browser/frame_host/navigation_request.cc b/content/browser/frame_host/navigation_request.cc
index 95bc35fb3f83407c51ba0257e2780d0dfe8694d3..5ed66ed0fc29f4af4d993bb2a3ccba815cb9e8fa 100644
--- a/content/browser/frame_host/navigation_request.cc
+++ b/content/browser/frame_host/navigation_request.cc
@@ -553,6 +553,18 @@ void NavigationRequest::OnRequestRedirected(
     }
   }
 
+  // Compute the SiteInstance to use for the redirect and pass its
+  // RenderProcessHost if it has a process. Keep a reference if it has a
+  // process, so that the SiteInstance and its associated process aren't deleted
+  // before the navigation is ready to commit.
+  scoped_refptr<SiteInstance> site_instance =
+      frame_tree_node_->render_manager()->GetSiteInstanceForNavigationRequest(
+          *this);
+  RenderProcessHost* expected_process =
+      site_instance->HasProcess() ? site_instance->GetProcess() : nullptr;
+  speculative_site_instance_ =
+      site_instance->HasProcess() ? site_instance : nullptr;

[clamy, 2017/06/27 16:43:32]

Note: I'm not storing the SiteInstance if its process is not initialized,
because I'm worried that someone could carelessly call GetProcess on it and
trigger an unwanted process initialization. Since we don't need to keep its
process alive (the motivation for storing it), I'd rather we don;t store it in
that case.

[Charlie Reis, 2017/06/27 18:46:34]

Acknowledged.

+
   // It's safe to use base::Unretained because this NavigationRequest owns the
   // NavigationHandle where the callback will be stored.
   bool is_external_protocol =
@@ -560,7 +572,7 @@ void NavigationRequest::OnRequestRedirected(
   navigation_handle_->WillRedirectRequest(
       common_params_.url, common_params_.method, common_params_.referrer.url,
       is_external_protocol, response->head.headers,
-      response->head.connection_info,
+      response->head.connection_info, expected_process,
       base::Bind(&NavigationRequest::OnRedirectChecksComplete,
                  base::Unretained(this)));
 }