Factor PageLoadTracker into its own header and impl files.

chrome/browser/page_load_metrics/page_load_metrics_embedder_interface.h

+// 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_PAGE_LOAD_METRICS_EMBEDDER_INTERFACE_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_EMBEDDER_INTERFACE_H_
+
+class GURL;
+
+namespace content {
+class WebContents;
+}  // namespace content
+
+namespace page_load_metrics {
+
+class PageLoadTracker;
+
+// This class serves as a functional interface to various chrome// features.
+// Impl version is defined in chrome/browser/page_load_metrics.
+class PageLoadMetricsEmbedderInterface {
+ public:
+  virtual ~PageLoadMetricsEmbedderInterface() {}
+  virtual bool IsPrerendering(content::WebContents* web_contents) = 0;
+  virtual bool IsNewTabPageUrl(const GURL& url) = 0;
+  virtual void RegisterObservers(PageLoadTracker* metrics) = 0;
+};
+
+}  // namespace page_load_metrics
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_EMBEDDER_INTERFACE_H_