feat: introduce puppeteer-firefox (#3628)

This adds a proof-of-concept of `puppeteer-firefox`.
This consists of two parts:
- `//experimental/juggler` - patches to apply to Firefox.
- `//experimental/puppeteer-firefox` - front-end code to
be merged with Puppeteer.

As things become more stable, we'll gradually move it out of
the experimental folder.

experimental/juggler/.cirrus.yml

@@ -0,0 +1,38 @@
+task:
+  timeout_in: 120m
+  env:
+    CIRRUS_WORKING_DIR: /usr/local/src
+    SOURCE: /usr/local/src/
+    GS_AUTH: ENCRYPTED[c4b5b0404f5bfdc1b663a1eb5b70f3187b5d470d02eec3265b06b8e0d30226781523630931c1da6db06714c0d359f71f]
+    PATH: /root/.cargo/bin:$PATH:$SOURCE/gcloud/google-cloud-sdk/bin
+    SHELL: /bin/bash
+  container:
+    dockerfile: Dockerfile
+    # image: ubuntu
+    cpu: 8
+    memory: 24
+  name: linux
+  # install_deps_script: apt-get update && apt-get install -y wget python clang llvm git curl
+  install_gcloud_script: ./scripts/install_gcloud.sh
+  check_gcloud_script:
+    - echo "REVISION: $(git rev-parse HEAD)"
+    - gsutil cp FIREFOX_SHA gs://juggler-builds/$(git rev-parse HEAD)/
+  clone_firefox_script: ./scripts/fetch_firefox.sh
+  apply_patches_script:
+    - cd $SOURCE/firefox
+    - git config --global user.name "cirrus-ci-builder"
+    - git config --global user.email "aslushnikov@gmail.com"
+    - git am ../patches/*
+    - ln -s $PWD/../juggler testing/juggler
+  bootstrap_firefox_script:
+    - cd $SOURCE/firefox
+    - ./mach bootstrap --application-choice=browser --no-interactive
+  build_firefox_script:
+    - cd $SOURCE/firefox
+    - ./mach build
+  package_firefox_script:
+    - cd $SOURCE/firefox
+    - ./mach package
+  upload_build_to_gcloud_script:
+    - bash $SOURCE/scripts/upload_linux.sh
+