This CL fixes usages of [EnforceRange] annotations in IDL files.
No changes on behaviors.

CSSUnitValue:
 [EnforceRange] can't annotate non-integer numbers, and the spec
 doesn't have the annotation.

OffscreenCanvas:
 The spec doesn't have [EnforceRange], but it seems the spec is wrong.
 (requesting to update the spec; https://github.com/whatwg/html/issues/3540)

IDBFactory and IDBIndex:
 Follows spec.

Test IDLs:
 This CL works for tests in Chromium repository, and following tests
 need to be upstream for WPT.
 - wpt/interfaces/IndexedDB.idl
 - wpt/interfaces/WebCryptoAPI.idl

Bug: 819112
Change-Id: If7082cba0251a83e269fea428340b3b61d4c17cf
Reviewed-on: https://chromium-review.googlesource.com/952589
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542375}