def execute(self, grpc_code_dir, gapic_code_dir):
        """Move the protos into the GAPIC structure.

        This copies the ``x/y/z/proto/`` directory over to be a sibling
        of ``x/y/z/gapic/`` in the GAPIC code directory. In the event of
        an inconsistency on the prefix, the GAPIC wins.

        Args:
            grpc_code_dir (str): The location where the GRPC code was
                generated.
            gapic_code_dir (str): The location where the GAPIC code was
                generated.
        """
        # Determine the appropriate source and target directory.
        # We can get this by drilling in to the GAPIC artifact until we get to
        # a "gapic" directory that is outside "docs" and "tests".
        src = self._get_proto_path(grpc_code_dir)
        target = self._get_gapic_subdir_path(gapic_code_dir)

        # Move the contents into the GAPIC directory.
        self.exec_command(['mv', src, os.path.join(target, 'proto')])

        # Create an __init__.py file in the proto directory.
        # This is necessary for Python 2.7 compatibility.
        self.exec_command([
            'touch', os.path.join(target, 'proto', '__init__.py'),
        ])

        # Remove the grpc directory.
        self.exec_command(['rm', '-rf', grpc_code_dir])

        # Clear out the grpc_code_dir, so future tasks perceive it as
        # not being a thing anymore.
        return {'grpc_code_dir': None}