Update viewport_meta setting on any navigation.

content/browser/frame_host/navigation_controller_impl.cc

Index: content/browser/frame_host/navigation_controller_impl.cc
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index 5bde4bb4340d76cb67cc37f410824c5a814269d9..c7e009d3ff39d8d004dc5ca29b775893ccea87f2 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -803,9 +803,14 @@ bool NavigationControllerImpl::RendererDidNavigate(
   is_initial_navigation_ = false;
 
   // Save the previous state before we clobber it.
+  bool overriding_user_agent_changed = false;
   if (GetLastCommittedEntry()) {
     details->previous_url = GetLastCommittedEntry()->GetURL();
     details->previous_entry_index = GetLastCommittedEntryIndex();
+    if (pending_entry_ &&
+        pending_entry_->GetIsOverridingUserAgent() !=
+            GetLastCommittedEntry()->GetIsOverridingUserAgent())
+      overriding_user_agent_changed = true;
   } else {
     details->previous_url = GURL();
     details->previous_entry_index = -1;
@@ -953,6 +958,9 @@ bool NavigationControllerImpl::RendererDidNavigate(
 
   NotifyNavigationEntryCommitted(details);
 
+  if (overriding_user_agent_changed)
+    delegate_->UpdateOverridingUserAgent();

[nasko, 2017/01/09 23:07:53]

Technically this should only be called if we actually committed a new page,
right? Regardless whether it is in session history or not. It seems more
appropriate to put it in the cases we know it will happen than just generically
here.

[aelias_OOO_until_Jul13, 2017/01/09 23:10:52]

Right.  Could you give me a more concrete suggestion of where I should put this
instead?  This was the most specific place I found, but I'm not too familiar
with this code.

[nasko, 2017/01/09 23:44:03]

Yes. The switch statement on 850 calls a specific method for each type of
navigation. History navigations are classified as NAVIGATION_TYPE_EXISTING_PAGE,
so you can put the code inside of RendererDidNavigateToExistingPage. It is also
pretty helpful that this method enforces through DCHECK that it is only called
for main frames, which fits the behavior of our case too. 

[aelias_OOO_until_Jul13, 2017/01/10 01:17:43]

OK, done.  Note that I needed to change the underlying entry lookup to
GetActiveEntry() because GetVisibleEntry() only changed in
NotifyNavigationEntryCommitted().

+
   // Update the nav_entry_id for each RenderFrameHost in the tree, so that each
   // one knows the latest NavigationEntry it is showing (whether it has
   // committed anything in this navigation or not). This allows things like