Add GrContextThreadSafeProxy and remove most friends of GrContextThreadSafeProxy

A step towards removing GrCaps from GrContext.h

Also adds operator== to GrContextThreadSafeProxy.

Change-Id: Ic0bae12299dfb0ac8817d9f1c56a1219d6df97d9
Reviewed-on: https://skia-review.googlesource.com/127329
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 8b79484..8f0d04b 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -71,6 +71,7 @@
   "$_src/gpu/GrColorSpaceXform.h",
   "$_src/gpu/GrContext.cpp",
   "$_src/gpu/GrContextPriv.h",
+  "$_src/gpu/GrContextThreadSafeProxyPriv.h",
   "$_src/gpu/GrCoordTransform.h",
   "$_src/gpu/GrDDLContext.cpp",
   "$_src/gpu/GrDefaultGeoProcFactory.cpp",