It doesn't change anything for now but it'll make the code much cleaner if we decide to use this type in a unittest.

Here's an example of how this data type should be used presently:
https://codereview.appspot.com/162100043/diff/70001/syzygy/agent/asan/registry_filter_unittest.cc (in RegistryFilterTest.AddCorruptRangeStackIds), it's ugly, we have to allocate a new AsanCorruptBlockRange object and never free it as we push it into a scoped vector...

It's slightly less efficient in term of memory and CPU, as we store a whole struct instead of just a pointer and we do a struct copy every time we push something into it, but it's only used at crash time....

BUG=
R=chrisha@chromium.org

Review URL: https://codereview.appspot.com/182130043