Revert of Revert of Return GrGLContext from GrTestTarget (patchset #1 id:1 of https://codereview.chromium.org/1211123004/)

Reason for revert:
un-referting, did not help DEPS roll

Original issue's description:
> Revert of Return GrGLContext from GrTestTarget (patchset #3 id:40001 of https://codereview.chromium.org/1207393002/)
>
> Reason for revert:
> speculative revert to unblock DEPS roll (layout-tests)
>
> Original issue's description:
> > Return GrGLContext from GrTestTarget
> >
> > BUG=skia:
> >
> > Committed: https://skia.googlesource.com/skia/+/b6d93ea428ca5d13641c35faca7d0380980a3a17
>
> TBR=bsalomon@google.com,joshualitt@google.com,joshualitt@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/1852ec2b46a2a0efbb3550ff4d8b640f56a810e9

TBR=bsalomon@google.com,joshualitt@google.com,joshualitt@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1215593002
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 98d0ffc..4872db7 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -109,8 +109,8 @@
                           const GrPipeline&,
                           const GrBatchTracker&) const override;
 
-    virtual const GrGLInterface* glInterfaceForTesting() const {
-        return this->glInterface();
+    const GrGLContext* glContextForTesting() const override {
+        return &this->glContext();
     }
 
 private:
@@ -300,7 +300,7 @@
 
     void unbindTextureFromFBO(GrGLenum fboTarget);
 
-    SkAutoTDelete<GrGLContext>  fGLContext;
+    SkAutoTUnref<GrGLContext>  fGLContext;
 
     void createCopyProgram();