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/State.cpp b/src/libANGLE/State.cpp
index fd2abe1..08a6b8c 100644
--- a/src/libANGLE/State.cpp
+++ b/src/libANGLE/State.cpp
@@ -889,22 +889,12 @@
     }
 }
 
-Framebuffer *State::getReadFramebuffer()
+Framebuffer *State::getReadFramebuffer() const
 {
     return mReadFramebuffer;
 }
 
-Framebuffer *State::getDrawFramebuffer()
-{
-    return mDrawFramebuffer;
-}
-
-const Framebuffer *State::getReadFramebuffer() const
-{
-    return mReadFramebuffer;
-}
-
-const Framebuffer *State::getDrawFramebuffer() const
+Framebuffer *State::getDrawFramebuffer() const
 {
     return mDrawFramebuffer;
 }