Introduce stub microdump processor classes.

Adds the interfaces for MicrodumpProcessor (very similar to
MinidumpProcessor) and corresponding unittest stubs.
These stubs are required for multi-side integration and to start
rolling the updated processor library into the dependent projects.

BUG=chromium:410294



git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1372 4c0a9323-5329-0410-9bdc-e9ce6186880e
Update processor.gyp file with new files added as part of microdump
processing upcoming implementation.

dump_context.cc and dump_object.cc added in r/1370
microdump_processor.cc and microdump_processor_unittest.cc added in
r/1372

BUG=chromium:410294



git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1373 4c0a9323-5329-0410-9bdc-e9ce6186880e