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/renderer/FramebufferImpl.h b/src/libANGLE/renderer/FramebufferImpl.h
index 896f061..1681205 100644
--- a/src/libANGLE/renderer/FramebufferImpl.h
+++ b/src/libANGLE/renderer/FramebufferImpl.h
@@ -49,6 +49,8 @@
 
     virtual gl::Error invalidate(size_t count, const GLenum *attachments) = 0;
     virtual gl::Error invalidateSub(size_t count, const GLenum *attachments, const gl::Rectangle &area) = 0;
+
+    virtual GLenum checkStatus() const = 0;
 };
 
 }