Work on Windows GN component build.
This makes ppapi_shared link. This required many changes to gpu to match the structure of GYP in both component and non-component modes.
BUG=470212
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:android_chromium_gn_compile_dbg,android_chromium_gn_compile_rel;tryserver.chromium.win:win8_chromium_gn_rel,win8_chromium_gn_dbg;tryserver.chromium.mac:mac_chromium_gn_rel,mac_chromium_gn_dbg
Reland of https://codereview.chromium.org/
1053203003/
Review URL: https://codereview.chromium.org/
1061953002
Cr-Commit-Position: refs/heads/master@{#323966}