media: Drop "media::" in media/gpu

Now media/gpu is moved to media namespace, there's no need to use
media:: anymore.

BUG=586386

Review-Url: https://codereview.chromium.org/2061823003
Cr-Commit-Position: refs/heads/master@{#399790}

• media/gpu/android_copying_backing_strategy.cc[diff]
• media/gpu/android_copying_backing_strategy.h[diff]
• media/gpu/android_deferred_rendering_backing_strategy.cc[diff]
• media/gpu/android_deferred_rendering_backing_strategy.h[diff]
• media/gpu/android_video_decode_accelerator.cc[diff]
• media/gpu/android_video_decode_accelerator.h[diff]
• media/gpu/android_video_decode_accelerator_unittest.cc[diff]
• media/gpu/android_video_encode_accelerator.cc[diff]
• media/gpu/android_video_encode_accelerator.h[diff]
• media/gpu/avda_codec_image.cc[diff]
• media/gpu/avda_codec_image.h[diff]
• media/gpu/avda_return_on_failure.h[diff]
• media/gpu/avda_shared_state.cc[diff]
• media/gpu/avda_shared_state.h[diff]
• media/gpu/avda_state_provider.h[diff]
• media/gpu/dxva_picture_buffer_win.cc[diff]
• media/gpu/dxva_picture_buffer_win.h[diff]
• media/gpu/dxva_video_decode_accelerator_win.cc[diff]
• media/gpu/dxva_video_decode_accelerator_win.h[diff]
• media/gpu/fake_video_decode_accelerator.cc[diff]
• media/gpu/fake_video_decode_accelerator.h[diff]
• media/gpu/generic_v4l2_device.cc[diff]
• media/gpu/gpu_video_decode_accelerator_factory_impl.cc[diff]
• media/gpu/gpu_video_decode_accelerator_factory_impl.h[diff]
• media/gpu/h264_decoder.cc[diff]
• media/gpu/h264_decoder.h[diff]
• media/gpu/h264_dpb.cc[diff]
• media/gpu/h264_dpb.h[diff]
• media/gpu/ipc/common/create_video_encoder_params.cc[diff]
• media/gpu/ipc/common/create_video_encoder_params.h[diff]
• media/gpu/ipc/service/gpu_jpeg_decode_accelerator.cc[diff]
• media/gpu/ipc/service/gpu_jpeg_decode_accelerator.h[diff]
• media/gpu/ipc/service/gpu_video_decode_accelerator.cc[diff]
• media/gpu/ipc/service/gpu_video_decode_accelerator.h[diff]
• media/gpu/ipc/service/gpu_video_encode_accelerator.cc[diff]
• media/gpu/ipc/service/gpu_video_encode_accelerator.h[diff]
• media/gpu/ipc/service/media_channel.cc[diff]
• media/gpu/ipc/service/media_channel.h[diff]
• media/gpu/jpeg_decode_accelerator_unittest.cc[diff]
• media/gpu/shared_memory_region.cc[diff]
• media/gpu/shared_memory_region.h[diff]
• media/gpu/v4l2_device.cc[diff]
• media/gpu/v4l2_device.h[diff]
• media/gpu/v4l2_image_processor.cc[diff]
• media/gpu/v4l2_image_processor.h[diff]
• media/gpu/v4l2_jpeg_decode_accelerator.cc[diff]
• media/gpu/v4l2_jpeg_decode_accelerator.h[diff]
• media/gpu/v4l2_slice_video_decode_accelerator.cc[diff]
• media/gpu/v4l2_slice_video_decode_accelerator.h[diff]
• media/gpu/v4l2_video_decode_accelerator.cc[diff]
• media/gpu/v4l2_video_decode_accelerator.h[diff]
• media/gpu/v4l2_video_encode_accelerator.cc[diff]
• media/gpu/v4l2_video_encode_accelerator.h[diff]
• media/gpu/vaapi_jpeg_decode_accelerator.cc[diff]
• media/gpu/vaapi_jpeg_decode_accelerator.h[diff]
• media/gpu/vaapi_jpeg_decoder.cc[diff]
• media/gpu/vaapi_jpeg_decoder.h[diff]
• media/gpu/vaapi_jpeg_decoder_unittest.cc[diff]
• media/gpu/vaapi_video_decode_accelerator.cc[diff]
• media/gpu/vaapi_video_decode_accelerator.h[diff]
• media/gpu/vaapi_video_encode_accelerator.cc[diff]
• media/gpu/vaapi_video_encode_accelerator.h[diff]
• media/gpu/vaapi_wrapper.cc[diff]
• media/gpu/vaapi_wrapper.h[diff]
• media/gpu/video_decode_accelerator_unittest.cc[diff]
• media/gpu/video_encode_accelerator_unittest.cc[diff]
• media/gpu/vp8_decoder.cc[diff]
• media/gpu/vp8_decoder.h[diff]
• media/gpu/vp9_decoder.cc[diff]
• media/gpu/vp9_decoder.h[diff]
• media/gpu/vp9_picture.h[diff]
• media/gpu/vt_video_decode_accelerator_mac.cc[diff]
• media/gpu/vt_video_decode_accelerator_mac.h[diff]
• media/gpu/vt_video_encode_accelerator_mac.cc[diff]
• media/gpu/vt_video_encode_accelerator_mac.h[diff]