Refactor FFmpegVideoDecoder to try and generalize code common to all video decoders.

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index 17731213d0a85cf08e45ae653469cb0c551087ff..debbb2e56020f84b9558119ff34e0060d274f38c 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -52,6 +52,7 @@
         'base/buffer_queue.h',
         'base/buffers.cc',
         'base/buffers.h',
+        'base/callback.h',
         'base/clock.h',
         'base/clock_impl.cc',
         'base/clock_impl.h',
@@ -85,6 +86,8 @@
         'base/yuv_row_mac.cc',
         'base/yuv_row_linux.cc',
         'base/yuv_row.h',
+        'ffmpeg/ffmpeg_util.cc',
+        'ffmpeg/ffmpeg_util.h',
         'filters/audio_renderer_algorithm_base.cc',
         'filters/audio_renderer_algorithm_base.h',
         'filters/audio_renderer_algorithm_default.cc',
@@ -112,6 +115,7 @@
         'filters/file_data_source.h',
         'filters/null_audio_renderer.cc',
         'filters/null_audio_renderer.h',
+        'filters/video_decode_engine.h',
         'filters/video_renderer_base.cc',
         'filters/video_renderer_base.h',
       ],
@@ -182,6 +186,7 @@
         'base/mock_filters.cc',
         'base/mock_filters.h',
         'base/mock_reader.h',
+        'base/mock_task.h',
         'base/pipeline_impl_unittest.cc',
         'base/pts_heap_unittest.cc',
         'base/run_all_unittests.cc',
@@ -192,6 +197,7 @@
         'filters/audio_renderer_base_unittest.cc',
         'filters/ffmpeg_demuxer_unittest.cc',
         'filters/ffmpeg_glue_unittest.cc',
+        'filters/ffmpeg_video_decode_engine_unittest.cc',
         'filters/ffmpeg_video_decoder_unittest.cc',
         'filters/file_data_source_unittest.cc',
         'filters/video_renderer_base_unittest.cc',