Revert "Changes gl::RenderbufferStorage to rx::RenderbufferImpl"

This reverts commit 9fc51d90176dcf4273cd6689968e1ca5d1c9fe16.

Change-Id: I4134ebe5ef6b8f509f4cc5cc22a2d526ec43ef6d
Reviewed-on: https://chromium-review.googlesource.com/226374
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/FramebufferAttachment.cpp b/src/libGLESv2/FramebufferAttachment.cpp
index 894884a..540ede1 100644
--- a/src/libGLESv2/FramebufferAttachment.cpp
+++ b/src/libGLESv2/FramebufferAttachment.cpp
@@ -187,7 +187,7 @@
 
 GLsizei RenderbufferAttachment::getSamples() const
 {
-    return mRenderbuffer->getSamples();
+    return mRenderbuffer->getStorage()->getSamples();
 }
 
 GLuint RenderbufferAttachment::id() const