MinidumpCrashpadInfo: the default constructor should zero-initialize

MinidumpCrashpadInfo: the default constructor should zero-initialize.

This regressed in 359bdd86225c when a non-POD UUID data member was added
to MinidumpCrashpadInfo, which made MinidumpCrashpadInfo non-POD. This
problem seems to have affected MinidumpModuleCodeViewRecordPDB70 since
it was added, but it is not likely to have caused any problems there
because that structure never appears without having all of its members
populated. By comparison, MinidumpCrashpadInfo may be sparsely
populated.

This caused 4 of the 5 MinidumpCrashpadInfoWriter tests to fail on
Windows.

TEST=crashpad_minidump_test MinidumpCrashpadInfoWriter.*
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/94f7f9eeb2e6f6b56ef6546cd0dc720b4b45ce06

[Mark Mentovai, 2015-03-11 21:39:49]

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

[Robert Sesek, 2015-03-11 21:43:07]

LGTM. Per offline discussion, it's OK for these structs to not be POD. If we
wanted to make them POD, we should add a POD UUID type like uuid_t that is
convertible between the normal UUID type.

[Mark Mentovai, 2015-03-11 21:43:50]

Committed patchset #1 (id:1) manually as
94f7f9eeb2e6f6b56ef6546cd0dc720b4b45ce06 (presubmit successful).