[Runtime] Add the initialization for |app_component_|.

This patch is to add the initialization in the constructor.

CID=220054

Related to XWALK-2928.
(cherry picked from commit cff0b9f73256395fdd6055d97e151df318838d9b)

Conflicts:

	runtime/browser/xwalk_runner.cc
Merge pull request #2743 from wuhengzhi/crosswalk-10

[Runtime] Add the initialization for |app_component_|.