Add chrome.debugger.getTargets method to discover available debug targets.

chrome/test/data/extensions/api_test/debugger/background.js

 // Copyright (c) 2011 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.
 
 var pass = chrome.test.callbackPass;
 var fail = chrome.test.callbackFail;
 
 var tabId;
 var debuggee;
 var protocolVersion = "1.0";
 
+var SILENT_FLAG_REQUIRED = "Cannot attach to this target unless " +
+    "'silent-debugger-extension-api' flag is enabled.";
+
 chrome.test.runTests([
 
   function attachMalformedVersion() {
     chrome.tabs.getSelected(null, function(tab) {
       chrome.debugger.attach({tabId: tab.id}, "malformed-version",
           fail("Requested protocol version is not supported: malformed-version."));
     });
   },
 
   function attachUnsupportedMinorVersion() {
@@ skipping 77 matching lines @@
       chrome.tabs.remove(tab.id);
     });
   },
 
   function attachToMissing() {
     var missingDebuggee = {tabId: -1};
     chrome.debugger.attach(missingDebuggee, protocolVersion,
         fail("No tab with given id " + missingDebuggee.tabId + "."));
   },
 
-  function attachToExtensionWithNoSilentFlag() {
-    debuggeeExtension = {extensionId: "foo"};
+  function attachToOwnBackgroundPageWithNoSilentFlag() {
+    var ownExtensionId = chrome.extension.getURL('').split('/')[2];
+    debuggeeExtension = {extensionId: ownExtensionId};
     chrome.debugger.attach(debuggeeExtension, protocolVersion,
-        fail("Cannot attach to an extension unless " +
-            "'silent-debugger-extension-api' flag is enabled."));
+        fail(SILENT_FLAG_REQUIRED));
   }
 ]);