Add UMA to measure feasibility of making unique names immutable

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 7132bd367d88338464c8d1f69e1b07f75172e6f2..39aa40c081f5ac0905f11b19c817922631ae968d 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -2966,6 +2966,10 @@ void RenderFrameImpl::didChangeName(const blink::WebString& name,
         routing_id_, base::UTF16ToUTF8(base::StringPiece16(name)),
         base::UTF16ToUTF8(base::StringPiece16(unique_name))));
   }
+
+  if (!committed_first_load_) {

[Charlie Reis, 2016/10/01 00:05:12]

nit: No braces.

[dcheng, 2016/10/01 20:25:14]

Done.

+    name_changed_before_first_commit_ = true;
+  }
 }
 
 void RenderFrameImpl::didEnforceInsecureRequestPolicy(
@@ -3351,6 +3355,17 @@ void RenderFrameImpl::didCommitProvisionalLoad(
                "id", routing_id_,
                "url", GetLoadingUrl().possibly_invalid_spec());
   DCHECK_EQ(frame_, frame);
+
+  // TODO(dcheng): Remove this UMA once we have enough measurements.
+  if (!committed_first_load_ && !current_history_item_.isNull()) {

[Charlie Reis, 2016/10/01 00:05:12]

Why isn't current_history_item_ enough (here and above)?  Seems like they're
both only set in this method.

[dcheng, 2016/10/01 20:25:14]

I added a comment to try to make the purpose clearer.

+    if (!IsMainFrame()) {
+      UMA_HISTOGRAM_BOOLEAN(
+          "SessionRestore.SubFrameUniqueNameChangedBeforeFirstCommit",
+          name_changed_before_first_commit_);
+    }
+    committed_first_load_ = true;
+  }
+
   DocumentState* document_state =
       DocumentState::FromDataSource(frame->dataSource());
   NavigationStateImpl* navigation_state =