Reland "Fix unused variable "useSwiftShader"" This is a reland of d721cdefdcf4c3e62ae364f0dc525e3ca54042a3 Adding a missing include. Original change's description: > Fix unused variable "useSwiftShader" > > -Wunused-but-set-variable when rolling into Chromium crrev.com/c/3293895 > > Bug: angleproject:6496 > Change-Id: I02f7de303b52319c6a1821d7b697b7ee9bea8f89 > Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3292034 > Reviewed-by: Tim Van Patten <timvp@google.com> > Commit-Queue: Tim Van Patten <timvp@google.com> Bug: angleproject:6496 Change-Id: Id39e10a8f343600ea6b2f023442b4d8c7e1856dc Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3292036 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Yuly Novikov <ynovikov@chromium.org>