Change GLGetProcAddress typedef to function returning function pointer

ui/gl/glx_api_unittest.cc

 // 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.
 
 #include <memory>
 
 #include "base/command_line.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gl/gl_glx_api_implementation.h"
 #include "ui/gl/gl_implementation.h"
@@ skipping 39 matching lines @@
   }
 
   static GLXContext FakeCreateContextAttribsARB(Display* dpy,
                                                 GLXFBConfig config,
                                                 GLXContext share_context,
                                                 int direct,
                                                 const int* attrib_list) {
     return static_cast<GLXContext>(nullptr);
   }
 
-  static void* GL_BINDING_CALL FakeGLGetProcAddress(const char *proc) {
+  static GLFunctionPointerType GL_BINDING_CALL
+  FakeGLGetProcAddress(const char* proc) {
     if (!strcmp("glXCreateContextAttribsARB", proc)) {
-      return reinterpret_cast<void *>(&FakeCreateContextAttribsARB);
+      return reinterpret_cast<GLFunctionPointerType>(
+          &FakeCreateContextAttribsARB);
     }
     return NULL;
   }
 
   static const char* GL_BINDING_CALL FakeQueryExtensionsString(Display* dpy,
                                                                int screen) {
     return fake_extension_string_;
   }
 
  protected:
@@ skipping 35 matching lines @@
 
   base::CommandLine command_line(base::CommandLine::NO_PROGRAM);
   command_line.AppendSwitchASCII(switches::kDisableGLExtensions,
                                  kFakeDisabledExtensions);
   InitializeAPI(&command_line);
 
   EXPECT_STREQ(kFilteredExtensions, GetExtensions());
 }
 
 }  // namespace gl