Fail the web app manifest fetch if the document is sandboxed.

This ensures that sandboxed pages are regarded as non-PWAs, and that
other features in the browser process which trust the web manifest do
not receive the manifest at all if the document itself cannot access the
manifest.

BUG=771709

Change-Id: Ifd4d00c2fccff8cc0e5e8d2457bd55b992b0a8f4
Reviewed-on: https://chromium-review.googlesource.com/866529
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531121}
void ManifestUmaUtil::FetchSucceeded() {
  UMA_HISTOGRAM_ENUMERATION(kUMANameFetchResult,
                            MANIFEST_FETCH_SUCCESS,
                            MANIFEST_FETCH_RESULT_TYPE_COUNT);
}

void ManifestUmaUtil::FetchSucceeded() {
  UMA_HISTOGRAM_ENUMERATION(kUMANameFetchResult,
                            MANIFEST_FETCH_SUCCESS,
                            MANIFEST_FETCH_RESULT_TYPE_COUNT);
}
