[Application] Add the check for return value of Begin().

This patch is to check the return value of Begin().

CID=194012
CID=194029

Related to XWALK-2928

(cherry picked from commit 997a8a3505c1dcf6441ad5e564be3367d26d59e1)
[Runtime] Add the initialization for the struct members.

This patch is to add the initialization for the members in FieldIds.

CID=220063

Related to XWALK-2928.

(cherry picked from commit 5822a3b071412bb9ecbe3b297734af3f054a3d2a)
extensions: Check GetString()'s return value.

CID=229802
CID=229803

(cherry picked from commit df87c52a8cc52082faf97bbbd9d509457ea8f1e6)
[Application] Add the initialization for |header_|.

This patch is to add the initialization for |header_| in the
constructor.

CID=194686

Related to XWALK-2928.

(cherry picked from commit b40940c6f1ca8125d37e2164795415f039413504)
Merge pull request #2735 from rakuco/cr10-cid-backports

crosswalk-10: Backport Coverity fixes.