bind-gen: Support generation of function definitions.

This is just a first step to support the code generation
of bindings callback functions.

Introduces CodeGenerationContext for convenience, and
also demonstrates make_common_local_vars().

Bug: 839389
Change-Id: I9ff49b4bfc6bd98e6b29687cc01f986c2baa01fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1855325
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709389}
6 files changed