Make Framebuffer::checkStatus non-const.

BUG=angleproject:1388

Change-Id: Ia9befba0c915c087f2fe0557d91060256f6d4950
Reviewed-on: https://chromium-review.googlesource.com/348955
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/ContextState.cpp b/src/libANGLE/ContextState.cpp
index 8af2527..2b39b44 100644
--- a/src/libANGLE/ContextState.cpp
+++ b/src/libANGLE/ContextState.cpp
@@ -7,6 +7,8 @@
 // Data.cpp: Container class for all GL relevant state, caps and objects
 
 #include "libANGLE/ContextState.h"
+
+#include "libANGLE/Framebuffer.h"
 #include "libANGLE/ResourceManager.h"
 
 namespace gl