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

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

Index: chrome/test/data/extensions/api_test/debugger_extension/background.js
diff --git a/chrome/test/data/extensions/api_test/debugger_extension/background.js b/chrome/test/data/extensions/api_test/debugger_extension/background.js
index 63101a85e3e860abd3fb67aab28d6c6f11c05d46..2ed14b6e8b3f99e6344cdbb42654b1f1f312717d 100644
--- a/chrome/test/data/extensions/api_test/debugger_extension/background.js
+++ b/chrome/test/data/extensions/api_test/debugger_extension/background.js
@@ -37,5 +37,19 @@ chrome.test.runTests([
     chrome.debugger.detach(debuggee,
         fail("Debugger is not attached to the extension with id: " +
             debuggee.extensionId + "."));
+  },
+
+  function discoverOwnExtension() {
+    chrome.debugger.getTargets(function(targets) {
+      var target = targets.filter(
+          function(t) {
+            return t.type == 'extension' && t.title == 'Extension Debugger';
+          })[0];
+      if (target) {
+        chrome.debugger.attach({targetId: target.id}, protocolVersion, pass());
+      } else {
+        chrome.test.fail("No extension found");
+      }
+    });
   }
 ]);