Remove dead DocumentState metrics tracking code

In https://codereview.chromium.org/2437863005, page_load_histograms,
which was the only consumer of this code, was removed. Now that the
page_load_histograms code has been removed, this code can be removed as
well.

BUG=657993
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2449553002
Cr-Commit-Position: refs/heads/master@{#429646}
diff --git a/content/renderer/render_frame_impl.h b/content/renderer/render_frame_impl.h
index 8e21346e..6e2b3b48 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -527,8 +527,7 @@
   void willSubmitForm(const blink::WebFormElement& form) override;
   void didCreateDataSource(blink::WebLocalFrame* frame,
                            blink::WebDataSource* datasource) override;
-  void didStartProvisionalLoad(blink::WebLocalFrame* frame,
-                               double triggering_event_time) override;
+  void didStartProvisionalLoad(blink::WebLocalFrame* frame) override;
   void didReceiveServerRedirectForProvisionalLoad(
       blink::WebLocalFrame* frame) override;
   void didFailProvisionalLoad(blink::WebLocalFrame* frame,