port 199bbdb4 (r32351)

  original commit message:
  Moves all files related to AST and scopes into ast/,
  and all files related to scanner & parser to parsing/.

  Also eliminates a couple of spurious dependencies.

BUG=

Review URL: https://codereview.chromium.org/1476353002

Cr-Commit-Position: refs/heads/master@{#32358}