[ChromeDriver] Add support for attaching multiple DevToolsEventListeners to a DevToolsClient.

chrome/test/chromedriver/chrome_impl.cc

Index: chrome/test/chromedriver/chrome_impl.cc
diff --git a/chrome/test/chromedriver/chrome_impl.cc b/chrome/test/chromedriver/chrome_impl.cc
index adbfab9acd04325df27646134fd2bff2f0540208..2e62d3a0434069e8fadfaaa0e0f40e1a19a2e55d 100644
--- a/chrome/test/chromedriver/chrome_impl.cc
+++ b/chrome/test/chromedriver/chrome_impl.cc
@@ -81,7 +81,8 @@ Status ChromeImpl::Init() {
   if (debugger_urls.empty())
     return Status(kUnknownError, "unable to discover open pages");
   client_.reset(new DevToolsClientImpl(
-      socket_factory_, debugger_urls.front(), dom_tracker_.get()));
+      socket_factory_, debugger_urls.front()));
+  client_->AddListener(dom_tracker_.get());
 
   // Perform necessary configuration of the DevTools client.
   // Fetch the root document node so that Inspector will push DOM node