[chromium] add missing include from previous checkin

git-svn-id: svn://svn.chromium.org/blink/trunk@82008 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/WebKit/chromium/public/WebSpellCheckClient.h

@@ -31,6 +31,8 @@
 #ifndef WebSpellCheckClient_h
 #define WebSpellCheckClient_h
 
+#include "WebString.h"
+
 namespace WebKit {
 
 class WebString;