Fix warnings from the Windows build.

Fix warnings from the Windows build.

These warnings are fatal in my GYP-generated debug build.
The warnings can be seen on Linux/Mac with -Wshorten-64-to-32.

R=mark@chromium.org

Committed: https://code.google.com/p/google-breakpad/source/detail?r=1264

[Lei Zhang (chromium)]

https://breakpad.appspot.com/944002/diff/1/src/processor/minidump.cc
File src/processor/minidump.cc (left):

https://breakpad.appspot.com/944002/diff/1/src/processor/minidump.cc#oldcode606
src/processor/minidump.cc:606: context_flags_ = context_flags;
We just set |context_flags_| on line 595.
|context_ppc64->context_flags| comes from |context_flags| on line 545.

https://breakpad.appspot.com/944002/diff/1/src/processor/minidump.cc
File src/processor/minidump.cc (right):

https://breakpad.appspot.com/944002/diff/1/src/processor/minidump.cc#newcode680
src/processor/minidump.cc:680: context_flags_ =
static_cast<uint32_t>(context_arm64->context_flags);
This block now matches the PPC64 block above.

[Mark Mentovai]

Wow, Breakpad’s been on fire lately. LGTM.

https://breakpad.appspot.com/944002/diff/1/src/processor/minidump.cc
File src/processor/minidump.cc (right):

https://breakpad.appspot.com/944002/diff/1/src/processor/minidump.cc#newcode680
src/processor/minidump.cc:680: context_flags_ =
static_cast<uint32_t>(context_arm64->context_flags);
thestig wrote:
> This block now matches the PPC64 block above.

That’s what I was going to ask for, but you already took care of it. Thanks.

[Lei Zhang (chromium)]

Committed patchset #1 manually as r1264 (presubmit successful).