Add page view analytics to Observatory

runtime/observatory/lib/src/app/page.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of app;
 
 /// A [Page] controls the user interface of Observatory. At any given time
 /// one page will be the current page. Pages are registered at startup.
 /// When the user navigates within the application, each page is asked if it
 /// can handle the current location, the first page to say yes, wins.
 abstract class Page extends Observable {
   final ObservatoryApplication app;
 
   @observable ObservatoryElement element;
   @observable ObservableMap args;
 
   Page(this.app);
 
   /// Called when the page is installed, this callback must initialize
   /// [element].
   void onInstall();
 
   /// Called when the page is uninstalled, this callback must clear
   /// [element].
   void onUninstall() {
     element = null;
   }
 
   /// Called when the page should update its state based on [uri].
-  /// NOTE: Only called when the page is installed.
   void visit(Uri uri, Map argsMap) {
     args = toObservable(argsMap);
+    Analytics.reportPageView(uri);
     _visit(uri);
   }
 
   // Overridden by subclasses.
   void _visit(Uri uri);
 
   /// Called to test whether this page can visit [uri].
   bool canVisit(Uri uri);
 }
 
@@ skipping 282 matching lines @@
   void _visit(Uri uri) {
     assert(element != null);
     assert(canVisit(uri));
     app.vm.getIsolate(uri.queryParameters['isolateId']).then((i) {
       (element as MetricsPageElement).isolate = i;
     });
   }
 
   bool canVisit(Uri uri) => uri.path == 'metrics';
 }