Add OpenGL context to Viewer.

tools/viewer/sk_app/win/GLWindowContext_win.h

Index: tools/viewer/sk_app/win/GLWindowContext_win.h
diff --git a/tools/viewer/sk_app/win/GLWindowContext_win.h b/tools/viewer/sk_app/win/GLWindowContext_win.h
new file mode 100644
index 0000000000000000000000000000000000000000..f30a805e7234a4374216ce3f96643bb53f5c26a1
--- /dev/null
+++ b/tools/viewer/sk_app/win/GLWindowContext_win.h
@@ -0,0 +1,37 @@
+
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef GLWindowContext_win_DEFINED
+#define GLWindowContext_win_DEFINED
+
+#include <windows.h>
+#include "../GLWindowContext.h"
+
+namespace sk_app {
+
+class GLWindowContext_win : public GLWindowContext {
+public:
+    friend GLWindowContext* GLWindowContext::Create(void* platformData, const DisplayParams&);
+
+    ~GLWindowContext_win() override;
+
+    void onSwapBuffers() override;
+
+    void onInitializeContext(void*, const DisplayParams&) override;
+    void onDestroyContext() override;
+
+private:
+    GLWindowContext_win(void*, const DisplayParams&);
+
+    HWND              fHWND;
+    HGLRC             fHGLRC;
+};
+
+
+}
+
+#endif