Added a smoke test for DevTools extension API (detailed API tests are in WebKit)

chrome/test/data/devtools/extensions/devtools_extension/devtools.js

+function output(msg) {
+  webInspector.console.addMessage(webInspector.console.Severity.Log, msg);
+}
+
+function test() {
+  var expectedAPIs = [
+    "console",
+    "inspectedWindow",
+    "network",
+    "panels"
+  ];
+
+  for (var i = 0; i < expectedAPIs.length; ++i) {
+    var api = expectedAPIs[i];
+    if (typeof chrome.experimental.devtools[api] !== "object") {
+      output("FAIL: API " + api + " is missing");
+      return;
+    }
+  }
+  if (typeof chrome.experimental.devtools.inspectedWindow.tabId !== "number") {
+    output("FAIL: chrome.experimental.inspectedWindow.tabId is not a number");
+    return;
+  }
+  output("PASS");
+}
+
+test();