Reenable ffmpegsumo, and also readd the use_system_ffmpeg flag.

third_party/ffmpeg/ffmpeg.gyp

 # Copyright (c) 2009 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.
 
 {
   'target_defaults': {
     'conditions': [
       ['OS!="linux" and OS!="freebsd"', {'sources/': [['exclude', '/linux/']]}],
       ['OS!="mac"', {'sources/': [['exclude', '/mac/']]}],
       ['OS!="win"', {'sources/': [['exclude', '/win/']]}],
     ],
     'variables': {
       # Since we are not often debugging FFmpeg, and performance is
       # unacceptable without optimization, freeze the optimizations to -O2.
       # If someone really wants -O1 , they can change these in their checkout.
       # If you want -O0, see the Gotchas in README.Chromium for why that
       # won't work.
       'debug_optimize': '2',
       'mac_debug_optimization': '2',
     },
   },
   'variables': {
     # Allow overridding the selection of which FFmpeg binaries to copy via an
     # environment variable.  Affects the ffmpeg_binaries target.
     'ffmpeg_branding%': '<(branding)',
     'ffmpeg_variant%': '<(target_arch)',
 
+    'use_system_ffmpeg%': 0,
+
     # Locations for generated artifacts.
     'shared_generated_dir': '<(SHARED_INTERMEDIATE_DIR)/third_party/ffmpeg',
     'asm_library': 'ffmpegasm',
   },
   'conditions': [
     # This condition is for migrating from pre-built binaries to an in-tree
     # source build.  Most of these should be removed once FFmpeg is built on
     # mac and linux.  Windows will take more work.
     #
     # TODO(ajwong): Per the comment above, reduce this conditional's size and
     # determine if in-tree build in Windows is tractable.
-    ['OS!="linux" or OS=="freebsd" or OS=="linux"', {
+    ['OS!="linux" or OS!="freebsd" or use_system_ffmpeg==0', {
       'variables': {
         'target_for_binaries': 'ffmpeg_binaries',
         'ffmpeg_include_root': 'include',
       },
     },{  # else OS=="linux"
       'variables': {
         'target_for_binaries': 'ffmpegsumo_nolink',
         'ffmpeg_include_root': 'source/patched-ffmpeg-mt',
       },
       'targets': [
@@ skipping 504 matching lines @@
               'binaries/<(ffmpeg_bin_dir)/avformat-52.dll',
               'binaries/<(ffmpeg_bin_dir)/avutil-50.dll',
             ],
           },
           'dependencies': ['../../build/win/system.gyp:cygwin'],
         }], ['OS=="linux" or OS=="freebsd"', {
               'variables': {
                 # TODO(ajwong): Clean this up after we've finished
                 # migrating to in-tree build.
                 'source_files': [
-                  # TODO(ajwong): Temporary revert to make tree green while
-                  # builder libraries are updated.
-                  'binaries/<(ffmpeg_bin_dir)/libavcodec.so.52',
-                  'binaries/<(ffmpeg_bin_dir)/libavformat.so.52',
-                  'binaries/<(ffmpeg_bin_dir)/libavutil.so.50',
                 ],
               },
         }], ['OS=="mac"', {
               # TODO(ajwong): These files are also copied in:
               # webkit/tools/test_shell/test_shell.gyp and
               # chrome/chrome.gyp
               # Need to consolidate the copies in one place. (BUG=23602)
               'variables': {
                 'source_files': [
                   'binaries/<(ffmpeg_bin_dir)/libavcodec.52.dylib',
@@ skipping 13 matching lines @@
       ],
     },
   ],
 }
 
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