Make document.activeElement work with OOPIF

content/browser/frame_host/frame_tree.cc

Index: content/browser/frame_host/frame_tree.cc
diff --git a/content/browser/frame_host/frame_tree.cc b/content/browser/frame_host/frame_tree.cc
index 3e94bbebd176f41e619783a5d6cc56e70dd29286..911ae0decc4bb50fcf5d04dbb6ab668349fbc1b1 100644
--- a/content/browser/frame_host/frame_tree.cc
+++ b/content/browser/frame_host/frame_tree.cc
@@ -270,15 +270,21 @@ FrameTreeNode* FrameTree::GetFocusedFrame() {
 }
 
 void FrameTree::SetFocusedFrame(FrameTreeNode* node) {
-  // If the focused frame changed across processes, send a message to the old
-  // focused frame's renderer process to clear focus from that frame and fire
-  // blur events.
-  FrameTreeNode* oldFocusedFrame = GetFocusedFrame();
-  if (oldFocusedFrame &&
-      oldFocusedFrame->current_frame_host()->GetSiteInstance() !=
-          node->current_frame_host()->GetSiteInstance()) {
-    DCHECK(SiteIsolationPolicy::AreCrossProcessFramesPossible());
-    oldFocusedFrame->current_frame_host()->ClearFocus();
+  std::set<SiteInstance*> frame_tree_site_instances;
+  ForEach(base::Bind(&CollectSiteInstances, &frame_tree_site_instances));
+
+  // Update the focused frame in all other SiteInstances.  If focus changes to
+  // a cross-process frame, this allows the old focused frame's renderer
+  // process to clear focus from that frame and fire blur events.  It also
+  // ensures that the latest focused frame is available in all renderers to
+  // compute document.activeElement.
+  for (const auto& instance : frame_tree_site_instances) {

[alexmos, 2015/11/04 21:53:59]

The last part of my test illustrates why it's now necessary to update the remote
focused frame in all SiteInstances in the tree: if you have A-embed-B-embed-C,
and switch focus from A to C, B needs to find out about that, since its
document.activeElement should now return the <iframe> element for C.  There are
probably optimizations for this (i.e., we may not need to notify leaf nodes),
but I just did this for simplicity.

[Charlie Reis, 2015/11/04 22:23:42]

Acknowledged.

+    if (instance != node->current_frame_host()->GetSiteInstance()) {
+      DCHECK(SiteIsolationPolicy::AreCrossProcessFramesPossible());
+      RenderFrameProxyHost* proxy =
+          node->render_manager()->GetRenderFrameProxyHost(instance);
+      proxy->SetFocusedFrame();
+    }
   }
 
   node->set_last_focus_time(base::TimeTicks::Now());