This removes the "resolve" parameter from Declare, since there's no case
where Scope analysis wouldn't make the same resolution decision the
parser can make here.

Other cleanup includes:
  - Replace some if statements with DCHECKS where they could never be hit
  - After the above, reordered some conditions for clarity
  - Remove or edit down old comments

Should be no change in behavior.

R=neis@chromium.org

Review-Url: https://codereview.chromium.org/2217973003
Cr-Commit-Position: refs/heads/master@{#38454}