Merge changes Ie84b8777,I90148d83,If85f8a12,Id8932aaa,I7e2c800b, ...

* changes:
  gn2bp: add .java to supported source files
  gn2bp: properly split sources and tool_files
  gn2bp: change tool_files to set
  gn2bp: remove another perfetto-specific hack
  gn2bp: pass response_file_contents into script via /dev/stdin
  gn2bp: store response_file_contents for action targets