[ci] Add sizebot to gh actions

ghstack-source-id: 3bbf6e62e8f8ba14b8523d07605d5d289c2f28f3
Pull Request resolved: #30380

.github/workflows/runtime_build_and_test.yml

@@ -515,3 +515,72 @@ jobs:
       - run: ./scripts/circleci/run_devtools_e2e_tests.js
         env:
           RELEASE_CHANNEL: experimental
+
+  # ----- SIZEBOT -----
+  download_base_build_for_sizebot:
+    name: Download base build for sizebot
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 18.20.1
+          cache: yarn
+          cache-dependency-path: yarn.lock
+      - name: Restore cached node_modules
+        uses: actions/cache@v4
+        id: node_modules
+        with:
+          path: scripts/release/node_modules
+          key: ${{ runner.arch }}-${{ runner.os }}-scripts-modules-${{ hashFiles('scripts/release/yarn.lock') }}
+      - run: yarn install --frozen-lockfile
+      - run: yarn install --frozen-lockfile
+        working-directory: scripts/release
+      - name: Download artifacts for base revision
+        run: |
+          git fetch origin main
+          GH_TOKEN=${{ github.token }} scripts/release/download-experimental-build-ghaction.js --commit=$(git merge-base HEAD origin/main) --allowBrokenCI
+          mv ./build ./base-build
+      # TODO: The `download-experimental-build` script copies the npm
+      # packages into the `node_modules` directory. This is a historical
+      # quirk of how the release script works. Let's pretend they
+      # don't exist.
+      - name: Delete extraneous files
+        run: rm -rf ./base-build/node_modules
+      - name: Display structure of build
+        run: ls -R base-build
+      - name: Archive base-build
+        uses: actions/upload-artifact@v4
+        with:
+          name: base-build
+          path: base-build
+
+  sizebot:
+    name: Run sizebot
+    needs: download_base_build_for_sizebot
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 18.20.1
+          cache: yarn
+          cache-dependency-path: yarn.lock
+      - name: Restore cached node_modules
+        uses: actions/cache@v4
+        id: node_modules
+        with:
+          path: "**/node_modules"
+          key: ${{ runner.arch }}-${{ runner.os }}-modules-${{ hashFiles('yarn.lock') }}
+      - run: yarn install --frozen-lockfile
+      - name: Restore archived base-build
+        uses: actions/download-artifact@v4
+        with:
+          path: base-build
+      - run: echo ${{ github.sha }} >> build/COMMIT_SHA
+      - run: node ./scripts/tasks/danger
+      - name: Archive sizebot results
+        uses: actions/upload-artifact@v4
+        with:
+          name: sizebot-message
+          path: sizebot-message.md