Expose content shell's remote debugging URL.

lib/src/runner/browser/browser.dart

Index: lib/src/runner/browser/browser.dart
diff --git a/lib/src/runner/browser/browser.dart b/lib/src/runner/browser/browser.dart
index 8c3fefcf587fd24787ba3d132f71f8a2f6940dd9..bdb67fd701813e7404f82fdd1678c759609dc35d 100644
--- a/lib/src/runner/browser/browser.dart
+++ b/lib/src/runner/browser/browser.dart
@@ -32,6 +32,14 @@ abstract class Browser {
   Future<Uri> get observatoryUrl =>
       throw new UnsupportedError("$name doesn't support Observatory.");
 
+  /// The remote debugger URL for this browser.
+  ///
+  /// This will throw an [UnsupportedError] for browsers that don't support
+  /// remote debugging, and return `null` if the remote debugging URL can't be
+  /// found.
+  Future<Uri> get remoteDebuggerUrl =>
+      throw new UnsupportedError("$name doesn't support remote debugging.");
+
   /// The underlying process.
   ///
   /// This will fire once the process has started successfully.