Begin implementing a debugger page in Observatory.

runtime/bin/vmservice/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.
@@ skipping 72 matching lines @@
     }
   }
 
   void _visit(String url) {
     assert(element != null);
     assert(canVisit(url));
     // ClassTree urls are 'class-tree/isolate-id', chop off prefix, leaving
     // isolate url.
     url = url.substring(_urlPrefix.length);
     /// Request the isolate url.
-    app.vm.get(url).then((i) {
+    app.vm.get(url).then((isolate) {
       if (element != null) {
         /// Update the page.
         ClassTreeElement page = element;
-        page.isolate = i;
+        page.isolate = isolate;
       }
     }).catchError((e) {
       Logger.root.severe('ClassTreePage visit error: $e');
     });
   }
 
   /// Catch all.
   bool canVisit(String url) => url.startsWith(_urlPrefix);
 }
 
+class DebuggerPage extends Page {
+  static const _urlPrefix = 'debugger/';
+
+  DebuggerPage(app) : super(app);
+
+  void onInstall() {
+    if (element == null) {
+      element = new Element.tag('debugger-page');
+    }
+  }
+
+  void _visit(String url) {
+    assert(element != null);
+    assert(canVisit(url));
+    // Debugger urls are 'debugger/isolate-id', chop off prefix, leaving
+    // isolate url.
+    url = url.substring(_urlPrefix.length);
+    /// Request the isolate url.
+    app.vm.get(url).then((isolate) {
+      if (element != null) {
+        /// Update the page.
+        DebuggerPageElement page = element;
+        page.isolate = isolate;
+      }
+    }).catchError((e) {
+        Logger.root.severe('Unexpected debugger error: $e');
+    });
+  }
+
+  /// Catch all.
+  bool canVisit(String url) => url.startsWith(_urlPrefix);
+}
+
 class ErrorViewPage extends Page {
   ErrorViewPage(app) : super(app);
 
   void onInstall() {
     if (element == null) {
       /// Lazily create page.
       element = new Element.tag('service-view');
     }
   }
 
@@ skipping 85 matching lines @@
   void _visit(String url) {
     assert(element != null);
     assert(canVisit(url));
     app.vm.get(_isolateId(url)).then((i) {
       (element as MetricsPageElement).isolate = i;
     });
   }
 
   bool canVisit(String url) => _matcher.hasMatch(url);
 }