Move bit_cast from base/macros.h to its own header

gpu/command_buffer/tests/gl_readback_unittest.cc

 // Copyright 2014 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 <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 #include <GLES2/gl2extchromium.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <cmath>
 
 #include "base/bind.h"
+#include "base/bit_cast.h"
 #include "base/location.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/thread_task_runner_handle.h"
 #include "gpu/command_buffer/tests/gl_manager.h"
 #include "gpu/command_buffer/tests/gl_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace gpu {
@@ skipping 287 matching lines @@
 
     glDeleteFramebuffers(1, &framebuffer);
     glDeleteTextures(1, &texture_id);
   }
 
   glDeleteBuffers(1, &vertex_buffer);
   glDeleteProgram(program);
 }
 
 }  // namespace gpu