Change clang-format's Chromium JavaScript defaults

Chromium is starting to use clang-format on more JavaScript.

In doing this, we discovered that our defaults were not doing a good job
differentiating between JS and C++.

This change moves some defaults to only apply to C++.
https://reviews.llvm.org/D28165

Patch from Dan Beam <dbeam@chromium.org>!

llvm-svn: 290930