clang-format: Refactor indentation behavior for multiple nested blocks.

This fixes a few oddities when formatting multiple nested JavaScript
blocks, e.g.:

Before:
  promise.then(
      function success() {
        doFoo();
        doBar();
      },
      [], function error() {
        doFoo();
        doBaz();
      });
  promise.then([],
               function success() {
                 doFoo();
                 doBar();
               },
               function error() {
    doFoo();
    doBaz();
  });

After:
  promise.then(
      function success() {
        doFoo();
        doBar();
      },
      [],
      function error() {
        doFoo();
        doBaz();
      });
  promise.then([],
               function success() {
                 doFoo();
                 doBar();
               },
               function error() {
                 doFoo();
                 doBaz();
               });

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@210097 91177308-0d34-0410-b5e6-96231b3b80d8