Move SkGLContext and some GrGLInterface implementations to skgputest module

BUG=skia:
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Committed: https://skia.googlesource.com/skia/+/fe3456cb006110d045b26ff3f8681b893a757b58

Review URL: https://codereview.chromium.org/1815823002
diff --git a/tests/ImageTest.cpp b/tests/ImageTest.cpp
index 15ee54c..8485fda 100644
--- a/tests/ImageTest.cpp
+++ b/tests/ImageTest.cpp
@@ -26,6 +26,8 @@
 #include "SkUtils.h"
 #include "Test.h"
 
+using sk_gpu_test::GrContextFactory;
+
 static void assert_equal(skiatest::Reporter* reporter, SkImage* a, const SkIRect* subsetA,
                          SkImage* b) {
     const int widthA = subsetA ? subsetA->width() : a->width();