Add Make[backend] calls for creating GrContexts

Docs-Preview: https://skia.org/?cl=26369
Bug: skia:
Change-Id: I460ee63e466f85b05918479f068a2e5ca2d70550
Reviewed-on: https://skia-review.googlesource.com/26369
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/tools/gpu/gl/GLTestContext.h b/tools/gpu/gl/GLTestContext.h
index f5afa31..701000e 100644
--- a/tools/gpu/gl/GLTestContext.h
+++ b/tools/gpu/gl/GLTestContext.h
@@ -75,6 +75,8 @@
         }
     }
 
+    sk_sp<GrContext> makeGrContext(const GrContextOptions& options) override;
+
 protected:
     GLTestContext();