添加测试web文件

www/webrtc/js/common.js

@@ -0,0 +1,12 @@
+function trace(text) {
+  // This function is used for logging.
+  if (text[text.length - 1] === '\n') {
+    text = text.substring(0, text.length - 1);
+  }
+  if (window.performance) {
+    var now = (window.performance.now() / 1000).toFixed(3);
+    console.log(now + ': ' + text);
+  } else {
+    console.log(text);
+  }
+}