Port crash_cache tool to Linux.

Review URL: http://codereview.chromium.org/17353

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@7939 0039d316-1c4b-4281-b951-d872f2087c98

• base/process_util.h[diff]
• base/process_util_posix.cc[diff]
• base/process_util_win.cc[diff]
• net/crash_cache.scons[diff]
• net/disk_cache/rankings.cc[diff]
• net/disk_cache/stress_cache.cc[diff]
• net/tools/crash_cache/crash_cache.cc[diff]