Do *not* make file handles inheritable on Windows.
Do *not* make file handles inheritable on Windows.

This is the cause of the pub failures to unpack a file that has
just been created. The problem is that another 7-zip process has
inherited the file handle for a file that we are still writing.
When we are done writing the file, we cannot use it because the
other process still keeps the handle.

R=sgjesse@google.com,rnystrom@google.com
BUG=dartbug.com/5910

Review URL: https://codereview.chromium.org//11230051

git-svn-id: a962b240025cf0577aa172e20f49ccb159ba6be1@13960 260f80e4-7a28-3924-810f-c04153c831b5

computmaxer/pub,dart-lang/pub,cjkao/dart-pub,dart-lang/pub,maxwellpeterson-wf/pub