text: #include "rewrite_gflags.h"
  Implements rewriter options as command-line options, using the Google "gflags" package.
  LRU size is potentially needed at factory construction time so it is exposed as a method.
  Apply the parsed options to the options and factory. Note that some of the command-line flags control how the factory is constructed, whereas others affect the rewriting options, and should be considered global defaults.
  Sets the rewrite level/list passed on the specified option names & values. The flag names are passed in to provide better error messages.
  False is returned if the values cannot be parsed.
  Determines whether a flag was explicitly set, as opposed to having its default value.