Enable cpplint for webrtc/examples and fix all uncovered cpplint errors.

webrtc/examples/peerconnection/client/linux/main_wnd.h

Index: webrtc/examples/peerconnection/client/linux/main_wnd.h
diff --git a/webrtc/examples/peerconnection/client/linux/main_wnd.h b/webrtc/examples/peerconnection/client/linux/main_wnd.h
index 1a910827689da1373ea8b218df71f1f231139729..e35d4dd8fa9b1ba54dfb3be9b7ce169a684f608f 100644
--- a/webrtc/examples/peerconnection/client/linux/main_wnd.h
+++ b/webrtc/examples/peerconnection/client/linux/main_wnd.h
@@ -8,8 +8,10 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef PEERCONNECTION_SAMPLES_CLIENT_LINUX_MAIN_WND_H_
-#define PEERCONNECTION_SAMPLES_CLIENT_LINUX_MAIN_WND_H_
+#ifndef WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_LINUX_MAIN_WND_H_
+#define WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_LINUX_MAIN_WND_H_
+
+#include <string>
 
 #include "webrtc/examples/peerconnection/client/main_wnd.h"
 #include "webrtc/examples/peerconnection/client/peer_connection_client.h"
@@ -115,4 +117,4 @@ class GtkMainWnd : public MainWindow {
   int draw_buffer_size_;
 };
 
-#endif  // PEERCONNECTION_SAMPLES_CLIENT_LINUX_MAIN_WND_H_
+#endif  // WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_LINUX_MAIN_WND_H_