[Application] widget_handler: Add the check for return value.

The return value for GetString() was not being checked.

CID=194059
BUG=XWALK-2928
[Application] package: Initialize |manifest_type_|.

The member varibale was not being initialized in the constructor.

CID=194663
BUG=XWALK-2928
[Application] xpk_package: Add the check for fseek()'s return value and initialzie for |zip_addr_|.

The return value for fseek() was not being checked.
The variable "zip_addr_" was not initialzied in the constructor.

CID=194011
CID=194023
CID=194686
BUG=XWALK-2928
[Application] application_widget_storage: Add the check for return value.

The return value for GetString() and GetBoolean() was not being checked
in SaveConfigInfoItem().

CID=194012
CID=194029
BUG=XWALK-2928
[Android] Replace the raw pointer with scoped_ptr.

The raw pointer |ret_val| will lead to memory leak. Define it with
scoped_ptr.

CID=194532
BUG=XWALK-2928
[Extensions] xwalk_extension_client: Add the check for Get() and Map().

The return value of Get() and Map() was not being checked in
OnPostMessageToJS().

CID=194043
CID=194046
BUG=XWALK-2928
[Android] Add the check for GetHeader().

The return value of GetHeader() was not being checked.
If user agent was invalid, assign it with crosswalk user agent.

CID=194058
BUG=XWALK-2928
[Runtime] xwalk_browser_main_parts: Initialize |extension_service_|.

The member variable was not being Initialized in the constructor.

CID=194750
BUG=XWALK-2928
[Runtime] xwalk_runtime_features: Initialize |experimental_features_enabled_| and |enabled|.

The member variable was not being initialized in the constructor.
The variable in the struct was not being initialized.

CID=194645
CID=194651
BUG=XWALK-2928
[Runtime] runtime_download_manager_delegate: Add the check for
CreateDirectory().

The return value of CreateDirectory() was not being checked in
GenerateFilename().

CID=194047
BUG=XWALK-2928