Fix trusted_mmap_test for Mac OS X on x86_64.
Fix trusted_mmap_test for Mac OS X on x86_64.

CheckMapping in trusted/service_runtime/osx/mmap_test_check.cc only examined
a single VM region, but in reality, the entire 40GB guard area was comprosed
of many contiguous 128MB regions with identical characteristics (at least on
Mac OS X 10.8). It now checks for a large contiguous region by probing
beginning at the test address. Like the Linux version of CheckMapping, it
allows a region to be larger than the expected region geometry by allowing the
start address to be lower than the expected start, and the end address to be
higher than the expected end.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3087
TEST=trusted_mmap_test
Review URL: https://codereview.chromium.org/12213095

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@10747 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client