Clarify/fix fullscreen semantics, and add GetScreenSize

ppapi/proxy/ppb_fullscreen_proxy.h

Index: ppapi/proxy/ppb_fullscreen_proxy.h
diff --git a/ppapi/proxy/ppb_fullscreen_proxy.h b/ppapi/proxy/ppb_fullscreen_proxy.h
index d68965a987cba1f5089e6dca830162bb83798713..0efc189f2e76b7297f3024aa36cce070c8dc1e2e 100644
--- a/ppapi/proxy/ppb_fullscreen_proxy.h
+++ b/ppapi/proxy/ppb_fullscreen_proxy.h
@@ -7,6 +7,7 @@
 
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_bool.h"
+#include "ppapi/c/pp_size.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/proxy/interface_proxy.h"
 
@@ -36,6 +37,9 @@ class PPB_Fullscreen_Proxy : public InterfaceProxy {
   void OnMsgSetFullscreen(PP_Instance instance,
                           PP_Bool fullscreen,
                           PP_Bool* result);
+  void OnMsgGetScreenSize(PP_Instance instance,
+                          PP_Bool* result,
+                          PP_Size* size);
 };
 
 }  // namespace proxy