[Runtime] xwalk_runtime_features: Initialize |experimental_features_enabled_| and |enabled|.
[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

(cherry picked from commit 62c5068fc1355fe04d20ec7e07cc519c5c161cff)

TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk