Add assertion on initialization sequence.

Add assertion on initialization sequence.

 The order at which to call the controller methods is:
1) Any method that change the configuration_ field
2) start
3) Any other method

 This change adds assertion that it is done correctly.
Committed: https://code.google.com/p/google-breakpad/source/detail?r=1085

[Mark Mentovai]

LGTM