Fix multiline-params being ignored by proxy natives

Multiline parameters in proxy natives would be ignored by the jni_generator
because the .* in the params portion of the proxy natives regex was not
matching on newlines. This CL adds the flag re.DOTALL so that dot matches
on newline which fixes the issue, and adds test coverage for this case.

Bug: 898261
Change-Id: I28f1fb3c57b39daff4d8bb1eb2bfba4a2f4d7adc
Reviewed-on: https://chromium-review.googlesource.com/c/1306694
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Aiden Benner <abenner@google.com>
Cr-Commit-Position: refs/heads/master@{#604331}
2 files changed