Make FramebufferAttachmentObject not refcountable

Re-land with a fix for an unitialized variable

Instead the refcount is done via callbacks. This allows Surface to
ignore this refcounting which will be useful in a follow-up CL.

BUG=angleproject:891

Change-Id: I1925ccaa4ce7b502b33088660d31c404b8313cb5
Reviewed-on: https://chromium-review.googlesource.com/293712
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/Renderbuffer.cpp b/src/libANGLE/Renderbuffer.cpp
index 02e067c..27508ac 100644
--- a/src/libANGLE/Renderbuffer.cpp
+++ b/src/libANGLE/Renderbuffer.cpp
@@ -151,4 +151,18 @@
     return GetInternalFormatInfo(mInternalFormat).stencilBits;
 }
 
+void Renderbuffer::onAttach()
+{
+    addRef();
+}
+
+void Renderbuffer::onDetach()
+{
+    release();
+}
+
+GLuint Renderbuffer::getId() const
+{
+    return id();
+}
 }