IosExceptionMinidumpGenerator::WriteThreadStream() should be refactored for clarity

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The |stack_memory| array that it uses should be an array of {frame_pointer, 
link_register} pairs that is later treated as bytes. Only complicating factor 
is that there's one extra pointer value sticking off the end; this could likely 
just be stored separately.

Original issue reported on code.google.com by [email protected] on 18 Nov 2013 at 3:50