Closure compiler warnings

[davido]

Recent version of google closure compiler issues warnings:

bazel-out/k8-fastbuild/bin/polygerrit-ui/app/gr-app.js:37200: ERROR - Missing type declaration.
     * @returns Returns the selected item(s). If the multi property is true,
       ^
  ProTip: "JSC_JSDOC_MISSING_TYPE_WARNING" or "jsdocMissingType" can be added to the `suppress` attribute of:
  //polygerrit-ui/app:polygerrit_ui_closure_lib

WARNING - Failed to resolve sourcemap: bazel-out/k8-fastbuild/bin/polygerrit-ui/app/web-animations-next-lite.min.js.map
  Codes: SOURCEMAP_RESOLVE_FAILED

bazel-out/k8-fastbuild/bin/polygerrit-ui/app/gr-app.js:37227: ERROR - Missing type declaration.
     * @returns Returns true if `item` is selected.
       ^
  ProTip: "JSC_JSDOC_MISSING_TYPE_WARNING" or "jsdocMissingType" can be added to the `suppress` attribute of:
  //polygerrit-ui/app:polygerrit_ui_closure_lib

bazel-out/k8-fastbuild/bin/polygerrit-ui/app/gr-app.js:37458: ERROR - Missing type declaration.
     * @returns Returns the index of the item
       ^
  ProTip: "JSC_JSDOC_MISSING_TYPE_WARNING" or "jsdocMissingType" can be added to the `suppress` attribute of:
  //polygerrit-ui/app:polygerrit_ui_closure_lib

To reproduce, clone gerrit code review, apply this series and run:

  $ bazel build :polygerrit