Add GLFW support for GrGLCreateNativeInterface

This file lets us use Skia's GPU backend with GLFW.
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1827153003
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Review URL: https://codereview.chromium.org/1827153003

cmake/CMakeLists.txt

@@ -93,6 +93,7 @@ remove_srcs(
     ../src/gpu/gl/SkCreatePlatformGLContext*.cpp     # For internal testing only.
     ../src/gpu/gl/command_buffer/*
     ../src/gpu/gl/egl/*
+    ../src/gpu/gl/glfw/*
     ../src/gpu/gl/iOS/*
     ../src/gpu/vk/*
     ../src/opts/SkBitmapProcState_opts_none.cpp

src/gpu/gl/glfw/GrGLCreateNativeInterface_glfw.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#include "gl/GrGLInterface.h"
+#include "gl/GrGLAssembleInterface.h"
+#include "gl/GrGLUtil.h"
+
+#include <GLFW/glfw3.h>
+
+static GrGLFuncPtr glfw_get(void* ctx, const char name[]) {
+    SkASSERT(nullptr == ctx);
+    SkASSERT(glfwGetCurrentContext());
+    return glfwGetProcAddress(name);
+}
+
+const GrGLInterface* GrGLCreateNativeInterface() {
+    if (nullptr == glfwGetCurrentContext()) {
+        return nullptr;
+    }
+
+    return GrGLAssembleInterface(nullptr, glfw_get);
+}