Currently jni_generator_helper.h includes a using statement for
JavaParamRef and ScopedJavaLocalRef. To allow this to be removed (since
it shouldn't really be there in a header file), add a "using" statement
to all the files currently depending on this.

BUG=568574
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2209993003
Cr-Commit-Position: refs/heads/master@{#409796}