MEMORY_BASIC_INFORMATION64 specifies an alignment of 16, but the
standard allocator used by containers doesn't honor this. Although 16
is the default alignment size used on Windows for x86_64, it's not for
32-bit x86. clang assumed that the alignment of the structure was as
declared, and used an SSE load sequence that required this alignment.
AlignedAllocator is a replacement for std::allocator that allows the
alignment to be specified. AlignedVector is an std::vector<> that uses
AlignedAllocator instead of std::allocator.
BUG=chromium:564691
R=scottmg@chromium.org
Review URL: https://codereview.chromium.org/1498133002 .