[Extensions] Move Extension::DisableReason to its own file

Bug:
Change-Id: I513ed197833c01fabe099d7d4df862b9f89c3e57

Move DisableReason enum out of the Extension class to its own file in
extensions/common/disable_reason.h. This allows sources to depend on the
disable reason enum without needing to depend on the Extension class
directly.

Change-Id: I513ed197833c01fabe099d7d4df862b9f89c3e57
Reviewed-on: https://chromium-review.googlesource.com/606553
Commit-Queue: Minh Nguyen <[email protected]>
Reviewed-by: Ilya Sherman <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Nicolas Zea <[email protected]>
Reviewed-by: Devlin <[email protected]>
Cr-Commit-Position: refs/heads/master@{#495694}
87 files changed