Fix for downstream android webview

Previously erros is struct sigcontext is not defined. Including the
header file now.

TBR=jln,markus
Android only include change. Android trybots pass compile.
NOTRY=true
BUG=

Review URL: https://chromiumcodereview.appspot.com/11636039

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@174104 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed