Record UMA stats for subframes history navigations.

content/browser/frame_host/navigator_impl.cc

Index: content/browser/frame_host/navigator_impl.cc
diff --git a/content/browser/frame_host/navigator_impl.cc b/content/browser/frame_host/navigator_impl.cc
index 93063b600cffe3aa9c0ea574b67ebeebd58a6a09..8ec2dc19173d35f3eda5416fe9a5ccc687973889 100644
--- a/content/browser/frame_host/navigator_impl.cc
+++ b/content/browser/frame_host/navigator_impl.cc
@@ -8,6 +8,7 @@
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "content/browser/frame_host/debug_urls.h"
 #include "content/browser/frame_host/frame_tree.h"
@@ -444,7 +445,8 @@ bool NavigatorImpl::NavigateToPendingEntry(
 }
 
 bool NavigatorImpl::NavigateNewChildFrame(
-    RenderFrameHostImpl* render_frame_host) {
+    RenderFrameHostImpl* render_frame_host,
+    const GURL& default_url) {
   NavigationEntryImpl* entry =
       controller_->GetEntryWithUniqueID(render_frame_host->nav_entry_id());
   if (!entry)
@@ -455,6 +457,26 @@ bool NavigatorImpl::NavigateNewChildFrame(
   if (!frame_entry)
     return false;
 
+  // Track how often history navigations load a different URL into a subframe
+  // than the frame's default URL.
+  bool restoring_different_url = frame_entry->url() != default_url;
+  UMA_HISTOGRAM_BOOLEAN("SessionRestore.RestoredSubframeURL",
+                        restoring_different_url);
+  // If this frame's unique name uses a frame path, record the name length.
+  // If these names are long in practice, then a proposed plan to truncate
+  // unique names might affect restore behavior, since it is complex to deal
+  // with truncated names inside frame paths.
+  if (restoring_different_url) {
+    const std::string& unique_name =
+        render_frame_host->frame_tree_node()->unique_name();
+    const char kFramePathPrefix[] = "<!--framePath ";
+    if (base::StartsWith(unique_name, kFramePathPrefix,
+                         base::CompareCase::SENSITIVE)) {
+      UMA_HISTOGRAM_COUNTS("SessionRestore.RestoreSubframeFramePathLength",
+                           unique_name.size());
+    }
+  }
+
   return NavigateToEntry(render_frame_host->frame_tree_node(), *frame_entry,
                          *entry, ReloadType::NONE, false, true, false, nullptr);
 }