Browser hang when playing video in popup window

The function "onShowCustomView" in WebChromeClient of subwebview is
not implemented, and makes the fullscreen layout can't be set. Here
we call main webview's onShowCustomView.

Change-Id: I576e017be61bca0775b5cc897f35092a63c6dca7
Author: weiweix.ji <weiweix.ji@intel.com>
Signed-off-by: Xiaokang Qin <xiaokang.qin@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 51736