The prebuilt files include `web/pdf_viewer.js` with some viewer APIs. Those are missing from type declarations.
),
        gulp
          .src(COMMON_WEB_FILES, { base: "web/" })
          .pipe(gulp.dest(CHROME_BUILD_CONTENT_DIR + "web")),
        gulp
          .src(
            ["web/locale/*/viewer.properties", "web/locale/locale.properties"],
            { base: "web/" }
          )
          .pipe(gulp.dest(CHROME_BUILD_CONTENT_DIR + "web")),
        createCMapBundle().pipe(
          gulp.dest(CHROME_BUILD_CONTENT_DIR + "web/cmaps")
        ),
        createStandardFontBundle().pipe(
          gulp.dest(CHROME_BUILD_CONTENT_DIR + "web/standard_fonts")
        ),
        preprocessHTML("web/viewer.html", defines).pipe(
          gulp.dest(CHROME_BUILD_CONTENT_DIR + "web")
        ),
        preprocessCSS("web/viewer.css", "chrome", defines, true)
          .pipe(
            postcss([autoprefixer({ overrideBrowserslist: ["chrome >= 68"] })])
          )
          .pipe(gulp.dest(CHROME_BUILD_CONTENT_DIR + "web")),
        gulp.src("LICENSE").pipe(gulp.dest(CHROME_BUILD_DIR)),
        gulp
          .src("extensions/chromium/manifest.json")
          .pipe(replace(/\bPDFJSSCRIPT_VERSION\b/g, version))
          .pipe(gulp.dest(CHROME_BUILD_DIR)),
        gulp