Open th32Process when enumerating processes.

PROCESSENTRY32 is the structure filled by Process32First/Process32Next,
and |th32Process| is the handle of the process to be opened for further
investigation.

The previous use of |th32ParentProcessID| have caused collecting a
redundant information about the parent process itself.

An example on how to enumerate child processes:
https://msdn.microsoft.com/library/windows/desktop/ms686701(v=vs.85).aspx

BUG=

Review-Url: https://codereview.chromium.org/2438023005
Cr-Commit-Position: refs/heads/master@{#429129}
1 file changed