Add page_load_metrics for css scanning experiment

chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..3cf6b07d5d437e11b03c5ca46d05bfe4d17c2f61
--- /dev/null
+++ b/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
@@ -0,0 +1,26 @@
+// Copyright 2016 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.
+
+#ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_CSS_SCANNING_PAGE_LOAD_METRICS_OBSERVER_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_CSS_SCANNING_PAGE_LOAD_METRICS_OBSERVER_H_
+
+#include "base/macros.h"
+#include "chrome/browser/page_load_metrics/page_load_metrics_observer.h"
+
+class CssScanningMetricsObserver
+    : public page_load_metrics::PageLoadMetricsObserver {
+ public:
+  CssScanningMetricsObserver();
+  ~CssScanningMetricsObserver() override;
+
+  // page_load_metrics::PageLoadMetricsObserver:
+  void OnFirstMeaningfulPaint(
+      const page_load_metrics::PageLoadTiming& timing,
+      const page_load_metrics::PageLoadExtraInfo& info) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CssScanningMetricsObserver);
+};
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_CSS_SCANNING_PAGE_LOAD_METRICS_OBSERVER_H_