Changes gl::RenderbufferStorage to rx::RenderbufferImpl

BUG=angle:782

Also eliminates Colorbuffer/DepthStencilBuffer and related friends
and adds the RenderbufferD3D implementation of RenderbufferImpl.

This version fixes problems with the prior CL's handling of
render target serial issuance.

Change-Id: I7ddfbec1097723d7ea6ce93a9c034f941349108a
Reviewed-on: https://chromium-review.googlesource.com/227195
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/libGLESv2.cpp b/src/libGLESv2/libGLESv2.cpp
index bc1b589..4a31f2c 100644
--- a/src/libGLESv2/libGLESv2.cpp
+++ b/src/libGLESv2/libGLESv2.cpp
@@ -3876,7 +3876,8 @@
             return;
         }
 
-        context->setRenderbufferStorage(width, height, internalformat, samples);
+        gl::Renderbuffer *renderbuffer = context->getState().getCurrentRenderbuffer();
+        renderbuffer->setStorage(width, height, internalformat, samples);
     }
 }
 
@@ -5821,7 +5822,8 @@
             return;
         }
 
-        context->setRenderbufferStorage(width, height, internalformat, samples);
+        gl::Renderbuffer *renderbuffer = context->getState().getCurrentRenderbuffer();
+        renderbuffer->setStorage(width, height, internalformat, samples);
     }
 }