Add MinidumpContext (X86 and AMD64 variants) and their writers

Add MinidumpContext (X86 and AMD64 variants) and their writers.

These are fairly simple classes and it’s not valuable to test them
individually. They will be tested as part of MinidumpThreadWriter and
MinidumpExceptionWriter.

R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/cb2288d1748c7cb51f0c934b51714e7b6d387967

[Mark Mentovai, 2014-09-22 19:53:34]

mark@chromium.org changed reviewers:
+ rsesek@chromium.org

[Robert Sesek, 2014-09-24 15:42:15]

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context.h
File minidump/minidump_context.h (right):

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context.h#...
minidump/minidump_context.h:30: //! \brief `CONTEXT_SERVICE_ACTIVE`.
Am I supposed to know what these mean?

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context.h#...
minidump/minidump_context.h:213: uint64_t p1_home;
What are these used for?

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context_wr...
File minidump/minidump_context_writer.h (right):

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context_wr...
minidump/minidump_context_writer.h:41: virtual size_t ContextSize() const = 0;
Why require this instead of just use SizeOfObject()?

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context_wr...
minidump/minidump_context_writer.h:64: //!     must only be modified while this
object is in the #kStateMutable state.
nit: 80cols

[Mark Mentovai, 2014-09-24 16:58:28]

I didn’t know what those architecture-independent CONTEXT_* things were about
either, because they weren’t really documented. I hunted them down and
documented them here.

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context_wr...
File minidump/minidump_context_writer.h (right):

https://codereview.chromium.org/593583004/diff/1/minidump/minidump_context_wr...
minidump/minidump_context_writer.h:41: virtual size_t ContextSize() const = 0;
rsesek wrote:
> Why require this instead of just use SizeOfObject()? 

SizeOfObject is protected, but code that comes across a MinidumpContextWriter
might want to know this.

This follows the same design that I used for MinidumpMemory, where we have
MemoryRangeSize().

[Robert Sesek, 2014-09-24 17:22:03]

LGTM

[Mark Mentovai, 2014-09-24 17:34:49]

Committed patchset #2 (id:20001) manually as cb2288d1748c (presubmit
successful).