Add a benchmark extension.

chrome/test/data/extensions/samples/benchmark/script.js

Index: chrome/test/data/extensions/samples/benchmark/script.js
===================================================================
--- chrome/test/data/extensions/samples/benchmark/script.js	(revision 0)
+++ chrome/test/data/extensions/samples/benchmark/script.js	(revision 0)
@@ -0,0 +1,28 @@
+// The port for communicating back to the extension.
+var benchmarkExtensionPort = chrome.extension.connect();
+
+// The url is what this page is known to the benchmark as.
+// The benchmark uses this id to differentiate the benchmark's
+// results from random pages being browsed.
+
+// TODO(mbelshe): If the page redirects, the location changed and the
+// benchmark stalls.
+var benchmarkExtensionUrl = window.location.toString();
+
+function sendTimesToExtension() {
+  var times = window.chromium.GetLoadTimes();
+  if (times.finishLoadTime != 0) {
+    benchmarkExtensionPort.postMessage({message: "load", url: benchmarkExtensionUrl, values: times});
+  } else {
+    window.setTimeout(sendTimesToExtension, 100);
+  }
+}
+
+function loadComplete() {
+  // Only trigger for top-level frames (e.g. the one we benchmarked)
+  if (window.parent == window) {
+    sendTimesToExtension();
+  }
+}
+
+window.addEventListener("load", loadComplete);