More robust stack walks when the IP address in the context frame is invalid (or not in a known module).

This is achieved by:
1. Extending the span of the scan for return address in the conext frame.  Initially, I wanted to extend the span of the scan for all frames but then I noticed that there is code for ARM already that is extending the search only for the context frame.  This kind of makes sense so I decided to reuse the same idea everywhere.
2. Attempting to restore the EBP chain after a successful scan for return address so that the stackwalker can switch back to FRAME_TRUST_CFI for the rest of the frames when possible.

I also fixed the lint errors in the files touched.
Review URL: https://breakpad.appspot.com/605002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1193 4c0a9323-5329-0410-9bdc-e9ce6186880e