Add Chromium backend build instructions

[svillar]

As the README.md file is already way too crowded we've decided to add them in a separate file at least until we don't reorganize the documentation.

Fixes #1437

[felipeerias]

I tried the instructions to compile Chromium from scratch and they were very incomplete. Perhaps we are better off telling people to follow the official guide to compile Chromium and then add our fork.

[svillar]

I tried the instructions to compile Chromium from scratch and they were very incomplete. Perhaps we are better off telling people to follow the official guide to compile Chromium and then add our fork.

Agree I totally forgot to add a link to the chromium official build instructions

[felipeerias]

The following sequence worked for me with a fresh install of Chromium.

Reference: https://chromium.googlesource.com/chromium/src/+/main/docs/linux/build_instructions.md

• Install depot tools and add them to the path
• mkdir chromium && cd chromium
• fetch --nohooks --no-history chromium
• edit ./.gclient

solutions = [
  {
    "name": "src",
    "url": "https://chromium.googlesource.com/chromium/src.git",
    "managed": False,
    "custom_deps": {},
    "custom_vars": {
      "checkout_pgo_profiles": True, 
    },
  },
]
target_os = ["android"]

• cd src
• gclient sync
• ./build/install-build-deps.sh --android
• gclient runhooks
• gn gen out/Default
• edit ./out/Default/args.gn (debug or release version)

target_os = "android"
target_cpu = "arm64"
is_official_build = true
ffmpeg_branding="Chrome"
proprietary_codecs=true

• git remote add wolvic-chromium https://github.com/Igalia/wolvic-chromium
• git fetch wolvic-chromium
  • git fetch --depth=1 wolvic-chromium to skip getting the history
  • alternatively, use something like git fetch --depth=1288 wolvic-chromium to get the commits that are new in our branch
• git switch wolvic
• autoninja -C out/Default content_aar ui_aar
  • here I had to add the PGO setting above and run gclient sync, and then compile again
• if that last command fails
  • run autoninja -C out/Default content/shell:content_shell_resources_grit
  • then run autoninja -C out/Default content_aar ui_aar again

After the compilation has finished successfully, continue with the steps to integrate the libraries into Wolvic.

• ./fix_aar.sh out/Default/Content.aar && ./fix_aar.sh out/Default/ChromiumUi.aar
• mkdir -p ${wolvic}/app/src/chromium/assets/
• cp *.aar ${wolvic}/app/src/chromium/assets/
  • that copies ChromiumUi.aar and Content.aar
• cp out/Default/snapshot_blob.bin ${wolvic}/app/src/chromium/assets/snapshot_blob_64.bin && cp out/Default/icudtl.dat ${wolvic}/app/src/chromium/assets/ && cp out/Default/wolvic.pak ${wolvic}/app/src/chromium/assets/
• update local.properties

chromium_aar=<LOCATION OF AAR FILES>

• sync Wolvic project with Gradle files
• pick one of the "Chromium" build variants

[felipeerias]

@svillar I have added a commit with more details about the process of downloading and building Chromium from scratch.