Rename Framebuffer::completeness to checkStatus and add an Impl method.

BUG=angle:841

Change-Id: I04b4ffd086424569a15aa21447dd552e0a898928
Reviewed-on: https://chromium-review.googlesource.com/232394
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/State.cpp b/src/libANGLE/State.cpp
index 0b8cbc6..cbe5576 100644
--- a/src/libANGLE/State.cpp
+++ b/src/libANGLE/State.cpp
@@ -1251,7 +1251,7 @@
       case GL_SAMPLES:
         {
             gl::Framebuffer *framebuffer = mDrawFramebuffer;
-            if (framebuffer->completeness(data) == GL_FRAMEBUFFER_COMPLETE)
+            if (framebuffer->checkStatus(data) == GL_FRAMEBUFFER_COMPLETE)
             {
                 switch (pname)
                 {