jni_generator: Support using fully qualified paths for header files.

This CL changes the jni_generator such that header files are
generated with the "jni_package/jni" portion of the path removed
when the jni_package variable isn't used.

This is necessary because future CLs will refactor JNI includes to
use fully qualified paths (relative to root_gen_dir), and these extra
path parts do not add anything except unnecessary verbosity.

Bug: 964169
Change-Id: I00f338abb0775ecab4633748d802ac0c01553a00
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1634726
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Eric Stevenson <estevenson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#670475}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 7d4937aa4749a20fc07d906026ce7a92561d4a9f
1 file changed