Revert "Revert "Bug 938171 - Browser Bookmark Migration to Homescreen in Gaia""

This reverts commit d35f1c9a22c87e96f0289135955f7316900de6ab.
Revert "Revert "Bug 938171 - Add app_migrator module include to bootstrap unit test""

This reverts commit 0acb88a5663af1fa4ec8beb84b7cb657acba19b2.
Bug 938171 - Add MockVersionHelper to bootstrap test for app_migrator module
Merge pull request #23294 from qdot/revert-revert-938171

Revert revert 938171