This change brings InstallDetails to the installer with the install mode
chosen on the basis of a command line switch. This makes InstallDetails
and various install_static APIs usable from within the installer.

A few calls to InstallUtil::IsChromeSxSProcess are also replaced with
values in kBrandConstants or other more correct/clear values.

BUG=373987

Review-Url: https://codereview.chromium.org/2459583002
Cr-Commit-Position: refs/heads/master@{#451769}