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/mock/MockTestContext.cpp b/tools/gpu/mock/MockTestContext.cpp
index 56cd68c..68941ad 100644
--- a/tools/gpu/mock/MockTestContext.cpp
+++ b/tools/gpu/mock/MockTestContext.cpp
@@ -10,6 +10,8 @@
 
 #include "MockTestContext.h"
 
+#include "GrContext.h"
+
 namespace {
 
 class MockTestContext : public sk_gpu_test::TestContext {
@@ -25,6 +27,10 @@
     void submit() override {}
     void finish() override {}
 
+    sk_sp<GrContext> makeGrContext(const GrContextOptions& options) override {
+        return GrContext::MakeMock(nullptr, options);
+    }
+
 protected:
     void teardown() override {}
     void onPlatformMakeCurrent() const override {}