Hi guys,
I solved this issue and want to share my method here.
First you need to make sure Chromium support H264 videos. You can add these two lines in your build arguments.
proprietary_codecs = true
ffmpeg_branding = "Chrome"
Unzip it and go to \depot_tools\chromium\src\third_party\widevine\cdm. Copy all the contents in this folder and make a new folder called win\x64. Paste all the files from \depot_tools\chromium\src\third_party\widevine\cdm and paste the unzip thing from zip file here.
After this you need to rebuild Chromium again and add these build agruments:
enable_widevine = true
bundle_widevine_cdm = true
ignore_missing_widevine_signing_cert = false
After you rebuild the Chromium, your Chromium can support protected content playback included Netflix Videos.
Best,
Bruce