Ensure Linux minidump writer flushes minidump header early.

Ensure Linux minidump writer flushes minidump header early.

If the Linux minidump writer crashes while writing a dump, the dump
might contain some useful information, but the header will be empty
because TypedMDRVA's destructor flushes the data, and the header var
doesn't go out of scope until the end of the `Dump` method. This
fixes that problem by putting the header in a shorter block scope.

We've seen this problem in some Android dumps in the wild, like:
https://crash-stats.mozilla.com/report/index/cef5b777-02d1-43c2-bf40-133ab2160209

R=thestig@chromium.org
BUG=https://bugzilla.mozilla.org/show_bug.cgi?id=1247978

Committed: https://chromium.googlesource.com/breakpad/breakpad/+/e5adfac03b410520a5ffc4a1adab570445d34e30

[Lei Zhang, 2016-02-12 19:35:21]

lgtm

[Ted Mielczarek, 2016-02-12 20:50:16]

Description was changed from

==========
Ensure Linux minidump writer flushes minidump header early.

If the Linux minidump writer crashes while writing a dump, the dump
might contain some useful information, but the header will be empty
because TypedMDRVA's destructor flushes the data, and the header var
doesn't go out of scope until the end of the `Dump` method. This
fixes that problem by putting the header in a shorter block scope.

We've seen this problem in some Android dumps in the wild, like:
https://crash-stats.mozilla.com/report/index/cef5b777-02d1-43c2-bf40-133ab216...

R=thestig@chromium.org
BUG=https://bugzilla.mozilla.org/show_bug.cgi?id=1247978
==========

to

==========
Ensure Linux minidump writer flushes minidump header early.

If the Linux minidump writer crashes while writing a dump, the dump
might contain some useful information, but the header will be empty
because TypedMDRVA's destructor flushes the data, and the header var
doesn't go out of scope until the end of the `Dump` method. This
fixes that problem by putting the header in a shorter block scope.

We've seen this problem in some Android dumps in the wild, like:
https://crash-stats.mozilla.com/report/index/cef5b777-02d1-43c2-bf40-133ab216...

R=thestig@chromium.org
BUG=https://bugzilla.mozilla.org/show_bug.cgi?id=1247978

Committed:
https://chromium.googlesource.com/breakpad/breakpad/+/e5adfac03b410520a5ffc4a...
==========

[Ted Mielczarek, 2016-02-12 20:50:18]

Committed patchset #1 (id:1) manually as
e5adfac03b410520a5ffc4a1adab570445d34e30 (presubmit successful).