Move app launch metric recording code from NTP to chrome/common.

chrome/common/extensions/extension_metrics.h

+// Copyright 2014 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_COMMON_EXTENSIONS_EXTENSION_METRICS_H_
+#define CHROME_COMMON_EXTENSIONS_EXTENSION_METRICS_H_
+
+#include "chrome/common/extensions/extension_constants.h"
+#include "extensions/common/manifest.h"
+
+namespace extensions {
+
+class Extension;
+
+// Records the given type of app launch for UMA.
+void RecordAppLaunchType(extension_misc::AppLaunchBucket bucket,
+                         extensions::Manifest::Type app_type);
+
+// Records an app launch from the search view of the app list.
+void RecordAppListSearchLaunch(const extensions::Extension* extension);
+
+// Records an app launch from the main view of the app list.
+void RecordAppListMainLaunch(const extensions::Extension* extension);
+
+// Records a web store launch in the appropriate histograms.
+void RecordWebStoreLaunch();
+
+}  // namespace extensions
+
+#endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_METRICS_H_