Revert of Revert of Remove now-unnecessary msvs_cygwin_shell (https://codereview.chromium.org/142953002/)

Reason for revert:
The MSVS generator is deprecated for Chromium.

You can try "set GYP_GENERATORS=ninja,msvs-ninja" which builds a VS project that shells to ninja for building, which might be helpful.

You can also still generate the msvs project via GYP_GENERATORS=msvs for browsing and editing, but it is no longer supported for building.

Original issue's description:
> Revert of Remove now-unnecessary msvs_cygwin_shell (https://codereview.chromium.org/139303024/)
> 
> Reason for revert:
> I can't build on Windows with MSVC... but when I revert this CL, I can at least get past this part of the build failure.
> 
> Lots of developers use MSVC... so please don't disable it.
> 
> Original issue's description:
> > Remove now-unnecessary msvs_cygwin_shell
> > 
> > Added https://src.chromium.org/viewvc/chrome?view=rev&revision=237636
> > but now unnecessary since we build on ninja everywhere.
> > 
> > TBR=wez@chromium.org
> > BUG=123026
> > 
> > Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=245747
> 
> TBR=wez@chromium.org,scottmg@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=123026
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=245856

TBR=wez@chromium.org,jar@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=123026

Review URL: https://codereview.chromium.org/142973002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245857 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245857