Add MGL entry points and port spinning_cube to use them

mojo/public/c/gpu/MGL/mgl.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Note: This header should be compilable as C.
+
+#ifndef MOJO_PUBLIC_C_GPU_MGL_MGL_H_
+#define MOJO_PUBLIC_C_GPU_MGL_MGL_H_
+
+#include <stdint.h>
+
+#include "mojo/public/c/gpu/MGL/mgl_types.h"
+#include "mojo/public/c/system/types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef uint32_t MGLOpenGLAPIVersion;
+
+// OpenGL ES 2.0
+#define MGL_API_VERSION_GLES2 ((MGLOpenGLAPIVersion)1)
+// OpenGL ES 3.0
+#define MGL_API_VERSION_GLES3 ((MGLOpenGLAPIVersion)2)
+// OpenGL ES 3.1
+#define MGL_API_VERSION_GLES31 ((MGLOpenGLAPIVersion)3)
+
+#define MGL_NO_CONTEXT ((MGLContext)0)
+
+struct MojoAsyncWaiter;
+
+// Creates a context at the given API version or returns MGL_NO_CONTEXT.
+// |command_buffer_handle| must be a command buffer message pipe handle from
+// the Gpu service or another source. The callee takes ownership of this
+// handle.
+// |share_group| specifies the share group to create this context in.
+// If this is MGL_NO_CONTEXT a new share group will be created for this context.
+// |lost_callback|, if not null, will be invoked when the context is lost.
+// |async_waiter| must be a pointer to a MojoAsyncWaiter implementation that is
+// usable from any thread the returned MGLContext will be used from
+// for as long as the context exists.
+MGLContext MGLCreateContext(MGLOpenGLAPIVersion version,
+                            MojoHandle command_buffer_handle,
+                            MGLContext share_group,
+                            MGLContextLostCallback lost_callback,
+                            void* lost_callback_closure,
+                            const struct MojoAsyncWaiter* async_waiter);
+void MGLDestroyContext(MGLContext context);
+
+// Makes |context| the current MGLContext for the calling thread. Calling with
+// MGL_NO_CONTEXT clears the current context.
+void MGLMakeCurrent(MGLContext context);
+
+// Returns the currently bound context for the calling thread or MGL_NO_CONTEXT
+// if there is none.
+MGLContext MGLGetCurrentContext(void);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // MOJO_PUBLIC_C_GPU_MGL_MGL_H_