Chrome Version       : 56.0.2914.3
OS Version: OS X 10.12.1

I think it needs to be CoreMIDI not CoreMidi

CoreMidi was added a while ago in r392969

$ build all
[1/276] LINK ./midi_unittests
FAILED: midi_unittests
export DEVELOPER_DIR=/Volumes/bdd/tapted/git/chromium/src/build/mac_files/Xcode.app;  TOOL_VERSION=1478048412 ../../build/toolchain/mac/linker_driver.py ../../third_party/llvm-build/Release+Asserts/bin/clang++  -stdlib=libc++ -arch x86_64 -isysroot /Volumes/bdd/tapted/git/chromium/src/build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -mmacosx-version-min=10.9 -Wl,-ObjC -Wl,-rpath,@loader_path/. -Wl,-rpath,@loader_path/../../.. -Wl,-pie -o "./midi_unittests" -Wl,-filelist,"./midi_unittests.rsp" ./libmidi.dylib ./libbase.dylib ./libbase_i18n.dylib ./libicui18n.dylib ./libicuuc.dylib -framework CoreMidi -framework AppKit
ld: framework not found CoreMidi
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Traceback (most recent call last):
  File "../../build/toolchain/mac/linker_driver.py", line 229, in <module>
    Main(sys.argv)
  File "../../build/toolchain/mac/linker_driver.py", line 79, in Main
    subprocess.check_call(compiler_driver_args)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 540, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['../../third_party/llvm-build/Release+Asserts/bin/clang++', '-stdlib=libc++', '-arch', 'x86_64', '-isysroot', '/Volumes/bdd/tapted/git/chromium/src/build/mac_files/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk', '-mmacosx-version-min=10.9', '-Wl,-ObjC', '-Wl,-rpath,@loader_path/.', '-Wl,-rpath,@loader_path/../../..', '-Wl,-pie', '-o', './midi_unittests', '-Wl,-filelist,./midi_unittests.rsp', './libmidi.dylib', './libbase.dylib', './libbase_i18n.dylib', './libicui18n.dylib', './libicuuc.dylib', '-framework', 'CoreMidi', '-framework', 'AppKit']' returned non-zero exit status 1
[194/198] STAMP obj/chrome/test/unit_tests_run.stamp
ninja: build stopped: cannot make progress due to previous errors.