Move SkGLContext and some GrGLInterface implementations to skgputest module

dm/DMSrcSink.cpp

Index: dm/DMSrcSink.cpp
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 1cffb3cfb574de16de5702b2c201e0e88290bb13..6647877168c3784e43597b5b8a8c29099af2abb8 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -45,6 +45,8 @@ DEFINE_bool(multiPage, false, "For document-type backends, render the source"
             " into multiple pages");
 DEFINE_bool(RAW_threading, true, "Allow RAW decodes to run on multiple threads?");
 
+using sk_gpu_test::GrContextFactory;
+
 namespace DM {
 
 GMSrc::GMSrc(skiagm::GMRegistry::Factory factory) : fFactory(factory) {}