Log UMA for navigation start timestamp skew for browser-initiated loads

content/renderer/render_frame_impl.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/render_frame_impl.h"
 
 #include <map>
 #include <string>
 
 #include "base/auto_reset.h"
@@ skipping 455 matching lines @@
 // stack.
 base::TimeTicks SanitizeNavigationTiming(
     blink::WebFrameLoadType load_type,
     const base::TimeTicks& browser_navigation_start,
     const base::TimeTicks& renderer_navigation_start) {
   if (load_type != blink::WebFrameLoadType::Standard)
     return base::TimeTicks();
   DCHECK(!browser_navigation_start.is_null());
   base::TimeTicks navigation_start =
       std::min(browser_navigation_start, renderer_navigation_start);
-  // TODO(csharrison) Investigate how big a problem the cross process
-  // monotonicity really is and on what platforms. Log UMA for:
-  // |renderer_navigation_start - browser_navigation_start|
+  base::TimeDelta difference =
+      renderer_navigation_start - browser_navigation_start;
+  if (difference > base::TimeDelta()) {
+    UMA_HISTOGRAM_TIMES("Navigation.Start.RendererBrowserDifference.Positive",
+                        difference);
+  } else {
+    UMA_HISTOGRAM_TIMES("Navigation.Start.RendererBrowserDifference.Negative",
+                        -difference);
+  }
   return navigation_start;
 }
 
 // PlzNavigate
 CommonNavigationParams MakeCommonNavigationParams(
     blink::WebURLRequest* request,
     bool should_replace_current_entry) {
   const RequestExtraData kEmptyData;
   const RequestExtraData* extra_data =
       static_cast<RequestExtraData*>(request->extraData());
@@ skipping 4863 matching lines @@
   mojo::ServiceProviderPtr service_provider;
   mojo::URLRequestPtr request(mojo::URLRequest::New());
   request->url = mojo::String::From(url);
   mojo_shell_->ConnectToApplication(request.Pass(), GetProxy(&service_provider),
                                     nullptr, nullptr,
                                     base::Bind(&OnGotContentHandlerID));
   return service_provider.Pass();
 }
 
 }  // namespace content