[chromedriver] Improve timeout behavior. Prompted by user who executes script on busy page.

chrome/test/chromedriver/chrome/devtools_client_impl_unittest.cc

Index: chrome/test/chromedriver/chrome/devtools_client_impl_unittest.cc
diff --git a/chrome/test/chromedriver/chrome/devtools_client_impl_unittest.cc b/chrome/test/chromedriver/chrome/devtools_client_impl_unittest.cc
index 4ccaa2db8407d4bf17799927d91e663d16941572..6e9fa558e1058479e0071d0853a98b55bf88203f 100644
--- a/chrome/test/chromedriver/chrome/devtools_client_impl_unittest.cc
+++ b/chrome/test/chromedriver/chrome/devtools_client_impl_unittest.cc
@@ -66,6 +66,8 @@ class MockSyncWebSocket : public SyncWebSocket {
   virtual SyncWebSocket::StatusCode ReceiveNextMessage(
       std::string* message,
       const base::TimeDelta& timeout) OVERRIDE {
+    if (timeout <= base::TimeDelta())
+      return SyncWebSocket::kTimeout;
     base::DictionaryValue response;
     response.SetInteger("id", id_);
     base::DictionaryValue result;