Make GrDrawContext be GrRenderTargetProxy-backed

This is split out of https://codereview.chromium.org/2215323003/ (Start using RenderTargetProxy (omnibus))

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3841

CQ_INCLUDE_TRYBOTS=master.client.skia.android:Test-Android-Clang-Nexus5-GPU-Adreno330-arm-Debug-GN_Android-Trybot

Change-Id: I1a47f19ed1ac0c249e6ccac8db74095d7f456db4
Reviewed-on: https://skia-review.googlesource.com/3841
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/include/private/GrTextureProxy.h b/include/private/GrTextureProxy.h
index 63cb3c8..5b4eeef 100644
--- a/include/private/GrTextureProxy.h
+++ b/include/private/GrTextureProxy.h
@@ -36,9 +36,9 @@
     // Wrapped version
     GrTextureProxy(sk_sp<GrTexture> tex);
 
-    // For wrapped textures we store it here.
-    // For deferred proxies we will fill this in when we need to instantiate the deferred resource
-    sk_sp<GrTexture> fTexture;
+    // For wrapped proxies the GrTexture pointer is stored in GrIORefProxy.
+    // For deferred proxies that pointer will be filled n when we need to instantiate
+    // the deferred resource
 
     typedef GrSurfaceProxy INHERITED;
 };