Revert "Changed NavigationController access to through tab in Java code"
This reverts commit 8b75c19b428805a0465624cd6047b705c3b9a1b5.
NavigationHandler was the interface proposed to handle all navigation related calls from chrome Java code for blimp and non-blimp mode uniformly. However, as of today most of these functionality can also be provided by Tab. For blimp 0.6 integration, this CL proposes to revert this interface and access the required call sites through tab, until a more concrete proposal of blimp navigation stack is presented.