Move the implementations of shader var init to the header. Making the contructors for shader variables inline saves us from exporting them across DLL boundaries. This makes it easier to use them in the translator when building the translator as a DLL. BUG=angle:466 Change-Id: Iee0556e06dc1f9e98fe9eea6577819305de0dd0b Reviewed-on: https://chromium-review.googlesource.com/198555 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Nicolas Capens <nicolascapens@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>