Add makeNotCurrent to TestContext

I find this useful for managing which context is active on threads.

Change-Id: I655955a2351f273751681f080190ca684d29db4e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270642
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/tools/gpu/mock/MockTestContext.cpp b/tools/gpu/mock/MockTestContext.cpp
index f892714..ec53193 100644
--- a/tools/gpu/mock/MockTestContext.cpp
+++ b/tools/gpu/mock/MockTestContext.cpp
@@ -31,6 +31,7 @@
 
 protected:
     void teardown() override {}
+    void onPlatformMakeNotCurrent() const override {}
     void onPlatformMakeCurrent() const override {}
     std::function<void()> onPlatformGetAutoContextRestore() const override { return nullptr; }
     void onPlatformSwapBuffers() const override {}