Switch RendererDidNavigateToSamePage to not use page id.

BUG=369661
TEST=everything stays green

Review URL: https://codereview.chromium.org/1212843005

Cr-Commit-Position: refs/heads/master@{#336781}
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index 850bdf5..2f8f8ea4 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -1193,11 +1193,10 @@
 void NavigationControllerImpl::RendererDidNavigateToSamePage(
     RenderFrameHostImpl* rfh,
     const FrameHostMsg_DidCommitProvisionalLoad_Params& params) {
-  // This mode implies we have a pending entry that's the same as an existing
-  // entry for this page ID. This entry is guaranteed to exist by
+  // This classification says that we have a pending entry that's the same as
+  // the last committed entry. This entry is guaranteed to exist by
   // ClassifyNavigation. All we need to do is update the existing entry.
-  NavigationEntryImpl* existing_entry = GetEntryWithPageID(
-      rfh->GetSiteInstance(), params.page_id);
+  NavigationEntryImpl* existing_entry = GetLastCommittedEntry();
 
   // We assign the entry's unique ID to be that of the new one. Since this is
   // always the result of a user action, we want to dismiss infobars, etc. like