<webview>: Add fullscreen permissionRequest API documentation.
<webview>: Add fullscreen permissionRequest API documentation.

BUG=141198
Test=The change can be previewed at:
https://chrome-apps-doc.appspot.com/_patch/1013383004/apps/tags/webview#type-FullscreenPermissionRequest
(I'm getting internal server error atm though)

Review URL: https://codereview.chromium.org/1013383004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#322061}

axinging/chromium-crosswalk,Just-D/chromium-1,PeterWangIntel/chromium-crosswalk,axinging/chromium-crosswalk,ltilve/chromium,ltilve/chromium,PeterWangIntel/chromium-crosswalk,Pluto-tv/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,hgl888/chromium-crosswalk,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,TheTypoMaster/chromium-crosswalk,Fireblend/chromium-crosswalk,Chilledheart/chromium,fujunwei/chromium-crosswalk,chuan9/chromium-crosswalk,Fireblend/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,Fireblend/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,ltilve/chromium,TheTypoMaster/chromium-crosswalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,chuan9/chromium-crosswalk,chuan9/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,PeterWangIntel/chromium-crosswalk,Just-D/chromium-1,Chilledheart/chromium,axinging/chromium-crosswalk,fujunwei/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,ltilve/chromium,Pluto-tv/chromium-crosswalk,ltilve/chromium,Fireblend/chromium-crosswalk,Just-D/chromium-1,Just-D/chromium-1,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,Chilledheart/chromium,chuan9/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,fujunwei/chromium-crosswalk,Just-D/chromium-1,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,Chilledheart/chromium,chuan9/chromium-crosswalk,Just-D/chromium-1,Fireblend/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,ltilve/chromium,Pluto-tv/chromium-crosswalk,fujunwei/chromium-crosswalk,ltilve/chromium,Fireblend/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,fujunwei/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,fujunwei/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,ltilve/chromium,axinging/chromium-crosswalk,Just-D/chromium-1,Chilledheart/chromium,TheTypoMaster/chromium-crosswalk,Fireblend/chromium-crosswalk,ltilve/chromium