Add new ref-counted Renderbuffer class.

Renderbuffers are a clear object type in GL, and this patch adds
a more consistent state representation for them. They're managed
by the ResourceManager, and have a storage implementation similar
to Textures, but much simpler.

BUG=angle:660

Change-Id: Ia17199bb8cb570d48db42e1f28ccbcc12a902fcf
Reviewed-on: https://chromium-review.googlesource.com/201834
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/Context.cpp b/src/libGLESv2/Context.cpp
index 1454538..93f3ae2 100644
--- a/src/libGLESv2/Context.cpp
+++ b/src/libGLESv2/Context.cpp
@@ -1066,7 +1066,7 @@
     return mResourceManager->getTexture(handle);
 }
 
-FramebufferAttachment *Context::getRenderbuffer(GLuint handle)
+Renderbuffer *Context::getRenderbuffer(GLuint handle)
 {
     return mResourceManager->getRenderbuffer(handle);
 }
@@ -1399,7 +1399,7 @@
         return;
     }
 
-    FramebufferAttachment *renderbufferObject = mState.renderbuffer.get();
+    Renderbuffer *renderbufferObject = mState.renderbuffer.get();
     renderbufferObject->setStorage(renderbuffer);
 }