rollup: fail on warnings (#4069)

Summary:
We’ve recently eliminated all Rollup warnings. This prevents regression.

Rollup upgrade needed for `--failAfterWarnings`, added recently:
<rollup/rollup#3712>

Test Plan:
Modify the `onwarn` handler in our `rollup_config.js` to remove any of
the early-`return`s, and note that `bazel build //tensorboard` fails.

wchargin-branch: rollup-no-warn

package.json

@@ -59,7 +59,7 @@
     "karma-sourcemap-loader": "^0.3.7",
     "prettier": "1.18.2",
     "requirejs": "^2.3.6",
-    "rollup": "^2.7.1",
+    "rollup": "^2.26.4",
     "sinon": "^7.4.1",
     "terser": "^4.6.3",
     "tslib": "^1.10.0",

tensorboard/defs/defs.bzl

@@ -33,6 +33,10 @@ def tf_js_binary(compile, deps, **kwargs):
     # Discard it.
     rollup_bundle(
         config_file = "//tensorboard/defs:rollup_config.js",
+        # Must pass `true` here specifically, else the input file argument to
+        # Rollup (added by `rollup_binary`) is interpreted as an option-value
+        # for `--failAfterWarnings`.
+        args = ["--failAfterWarnings", "true"],
         deps = deps + [
             "@npm//@rollup/plugin-commonjs",
             "@npm//@rollup/plugin-node-resolve",

yarn.lock

@@ -5089,10 +5089,10 @@ rimraf@^2.5.4, rimraf@^2.6.0, rimraf@^2.6.2, rimraf@^2.6.3:
   dependencies:
     glob "^7.1.3"
 
-rollup@^2.7.1:
-  version "2.23.0"
-  resolved "https://registry.yarnpkg.com/rollup/-/rollup-2.23.0.tgz#b7ab1fee0c0e60132fd0553c4df1e9cdacfada9d"
-  integrity sha512-vLNmZFUGVwrnqNAJ/BvuLk1MtWzu4IuoqsH9UWK5AIdO3rt8/CSiJNvPvCIvfzrbNsqKbNzPAG1V2O4eTe2XZg==
+rollup@^2.26.4:
+  version "2.26.4"
+  resolved "https://registry.yarnpkg.com/rollup/-/rollup-2.26.4.tgz#a8350fd6bd56fce9873a7db2bd9547d40de3992b"
+  integrity sha512-6+qsGuP0MXGd7vlYmk72utm1MrgZj5GfXibGL+cRkKQ9+ZL/BnFThDl0D5bcl7AqlzMjAQXRAwZX1HVm22M/4Q==
   optionalDependencies:
     fsevents "~2.1.2"