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

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

Index: chrome/test/data/extensions/api_test/debugger/background.js
diff --git a/chrome/test/data/extensions/api_test/debugger/background.js b/chrome/test/data/extensions/api_test/debugger/background.js
index d68ed6b02ea831aa9875cc418eda0f4bc38e94b0..140d2381ab0b35441000c80a917637a910e8bd9e 100644
--- a/chrome/test/data/extensions/api_test/debugger/background.js
+++ b/chrome/test/data/extensions/api_test/debugger/background.js
@@ -111,5 +111,37 @@ chrome.test.runTests([
     chrome.debugger.attach(debuggeeExtension, protocolVersion,
         fail("Cannot attach to an extension unless " +
             "'silent-debugger-extension-api' flag is enabled."));
+  },
+
+  function createAndDiscoverTab() {
+    chrome.test.listenOnce(chrome.tabs.onUpdated, function () {
+      chrome.debugger.getTargets(function(targets) {
+        var page = targets.filter(
+            function(t) {
+              return t.type == 'page' && t.title == 'Test page';
+            })[0];
+        if (page) {
+          chrome.debugger.attach(
+              {targetId: page.id}, protocolVersion, pass());
+        } else {
+          chrome.test.fail("Cannot discover a newly created tab");
+        }
+      });
+    });
+    chrome.tabs.create({url: "inspected.html"});
+  },
+
+  function discoverExtensionWithNoSilentFlag() {
+    chrome.debugger.getTargets(function(targets) {
+      var target = targets.filter(
+          function(target) { return target.type == 'extension'})[0];
+      if (target) {
+        chrome.debugger.attach({targetId: target.id}, protocolVersion,
+            fail("Cannot attach to an extension unless " +
+                "'silent-debugger-extension-api' flag is enabled."));
+      } else {
+        chrome.test.succeed();
+      }
+    });
   }
 ]);