[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.
Fix unit tests for widget handler

This patch is changing the way in which manifest
and application objects are created.
All below tests now pass:
 - WidgetHandlerTest.ParseManifestWithAllOfOtherItemsAndOnePreferenceItem
 - WidgetHandlerTest.ParseManifestWithAllOfOtherItemsAndThreePreferenceItemsList
 - WidgetHandlerTest.ParseManifestWithOnlyNameAndVersion
 - WidgetHandlerTest.ParseManifestWithInvalidAuthorHrefValue
Merge pull request #2696 from wuhengzhi/xwalk_2928_cid220063

[Runtime] Add the initialization for the struct members.
Merge pull request #2681 from aszafranek/WidgetHandlerTestFix

Fix unit tests for widget handler