UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/51.0.2679.0 Chrome/51.0.2679.0 Safari/537.36

Steps to reproduce the problem:
Attempt to build Chromium on arm64.

What is the expected behavior?

What went wrong?
Running gn fails due to duplicate object file names in ffmpeg. The output is as follows:

DEBUG:root:Running: /tmp/tmprrMMeZ/gn gen /«PKGBUILDDIR»/out/Release --args=treat_warnings_as_errors=false use_sysroot=false enable_nacl=false enable_nacl=false use_gold=false enable_hidpi=true enable_widevine=true fieldtrial_testing_like_official_build=true arm_use_neon=true target_cpu="arm64" use_cups=true  remove_webcore_debug_symbols=true is_clang=false is_debug=false
ERROR at //third_party/ffmpeg/BUILD.gn:126:1: Duplicate object file
source_set("ffmpeg_internal") {
^------------------------------
The target //third_party/ffmpeg:ffmpeg_internal
generates two object files with the same name:
  obj/third_party/ffmpeg/ffmpeg_internal/videodsp.o

It could be you accidentally have a file listed twice in the
sources. Or, depending on how your toolchain maps sources to
object files, two source files with the same name in different
directories could map to the same object file.

In the latter case, either rename one of the files or move one of
the sources to a separate source_set to avoid them both being in
the same target.

In third_party/ffmpeg/ffmpeg_generated.gni, for arm64, both line 152 and line 461 generate a file called videodsp.o, resulting in the conflict here.

Did this work before? N/A 

Chrome version: 51.0.2679.0  Channel: n/a
OS Version: 
Flash Version: