[ChromeDriver] Select the main frame if a non-existant child frame is targeted.

chrome/test/chromedriver/devtools_client_impl.cc

Index: chrome/test/chromedriver/devtools_client_impl.cc
diff --git a/chrome/test/chromedriver/devtools_client_impl.cc b/chrome/test/chromedriver/devtools_client_impl.cc
index e3eca4f8d647bd206ae526a54ac1b84009c98968..0779ee96dafe8514e1857f8f95052e198c023fa9 100644
--- a/chrome/test/chromedriver/devtools_client_impl.cc
+++ b/chrome/test/chromedriver/devtools_client_impl.cc
@@ -160,6 +160,16 @@ Status DevToolsClientImpl::ReceiveNextMessage(
     } else if (response->result) {
       cmd_response_map_[response->id] = response->result.release();
     } else {
+      scoped_ptr<base::Value> error(base::JSONReader::Read(response->error));
+      base::DictionaryValue* error_dict;
+      if (!error || !error->GetAsDictionary(&error_dict))
+        return Status(kUnknownError, "inspector error with no error code");
+      int error_code;
+      if (error_dict->GetInteger("code", &error_code) &&
+          error_code == internal::kContextIdNotFound) {
+        cmd_response_map_.erase(response->id);
+        return Status(kNoSuchFrame);
+      }
       return Status(kUnknownError, "inspector error: " + response->error);
     }
   }