Don't write duplicate gtest logs on iOS.

When running tests on iOS devices, test output is written to a file by
redirecting stdout/stderr. When the test completes the content of those
files is written to NSLog so they're accessible in the device's log.

This CL removes duplicate logging in the device's log by closing the
redirected files before writing to NSLog. Otherwise, the content
written to NSLog is redirected to the files.

BUG=227661

Review URL: https://codereview.chromium.org/142843003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249443 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249443