Include VS2013 runtime folders in PATH for automatic toolchain

Include VS2013 runtime folders in PATH for automatic toolchain

Reproduced on a new Win7 x64 VM, and this fixed the build (at
least for the chrome target).

This doesn't address the need to copy the runtime DLLs into the
output directory so that chrome runs though, that's a separate
problem where something in chrome's gyp should be copying them
there, at least for a debug build.

TBR=mikelawther@chromium.org
BUG=326345
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=239671

[scottmg, 2013-12-10 05:34:11]

Committed patchset #1 manually as r239671 (presubmit successful).

[Mike Lawther (Google), 2013-12-10 06:47:51]

lgtm. As I commented on the bug:

"I updated past r239671 (my checkout is now at r239683), and following my steps
in the OP now produces a working Release compile and build of content_shell.exe.
Yay!"