Add helpers to generate GEN_JNI.java during JNI registration

GEN_JNI contains the actual native method declaration
that corresponds to a method in an @JniNatives annotation.
This change adds helpers to generate GEN_JNI with all
proxy natives that are being registered in a generated
registration header file.

- Also fixes bug where hashed method names were escaped
one too many times.
- Adds better tests for special JNI type cases.

Change-Id: Ie705d0cf55233c513ad4bc32024212454115bcba
Bug: 898261
Reviewed-on: https://chromium-review.googlesource.com/c/1315687
Commit-Queue: Aiden Benner <abenner@google.com>
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608974}
9 files changed