Update a comment with a link to a historic source.

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 979b26c1dc5603b12adb1edc1907ea5a08cc41aa..2198e58618056466fbe4f8d2a3fd3d94ac0d3279 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -37,6 +37,7 @@
 #include "content/public/browser/user_metrics.h"
 #include "content/public/common/content_client.h"
 #include "content/public/common/content_constants.h"
+#include "content/public/common/content_switches.h"
 #include "net/base/escape.h"
 #include "net/base/mime_util.h"
 #include "net/base/net_util.h"
@@ -1225,7 +1226,22 @@ void NavigationControllerImpl::RendererDidNavigateNewSubframe(
     const FrameHostMsg_DidCommitProvisionalLoad_Params& params) {
   if (ui::PageTransitionCoreTypeIs(params.transition,
                                    ui::PAGE_TRANSITION_AUTO_SUBFRAME)) {
-    // This is not user-initiated. Ignore.
+    // There was a comment here that said, "This is not user-initiated. Ignore."
+    // But this makes no sense; non-user-initiated navigations should be
+    // determined to be of type NAVIGATION_TYPE_AUTO_SUBFRAME and sent to
+    // RendererDidNavigateAutoSubframe below.
+    //
+    // This if clause dates back to https://codereview.chromium.org/115919 and
+    // the handling of immediate redirects. TODO(avi): Is this still valid? I'm
+    // pretty sure that's there's nothing left of that code and that we should
+    // take this out.
+    //
+    // Except for cross-process iframes; this doesn't work yet for them.
+    if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kSitePerProcess)) {
+      NOTREACHED();
+    }
+
     DiscardNonCommittedEntriesInternal();
     return;
   }
@@ -1245,6 +1261,9 @@ void NavigationControllerImpl::RendererDidNavigateNewSubframe(
 bool NavigationControllerImpl::RendererDidNavigateAutoSubframe(
     RenderFrameHost* rfh,
     const FrameHostMsg_DidCommitProvisionalLoad_Params& params) {
+  DCHECK(ui::PageTransitionCoreTypeIs(params.transition,
+                                      ui::PAGE_TRANSITION_AUTO_SUBFRAME));

[Avi (use Gerrit), 2015/02/09 22:20:50]

Note that this fails on the reload tests because it comes through as
PAGE_TRANSITION_MANUAL_SUBFRAME. Do you think this is a bug?

[Charlie Reis, 2015/02/09 22:33:03]

It certainly seems strange for this check to fail given the method name.  I'm
not entirely sure what the intention was, but it seems like things would be
easier to understand if we did enforce this check.

+
   // We're guaranteed to have a previously committed entry, and we now need to
   // handle navigation inside of a subframe in it without creating a new entry.
   DCHECK(GetLastCommittedEntry());