Allocates almost all maps found in the start up snapshot into RO_SPACE.
There are 2 JSObject maps that are excluded as they contain a mutable cell.

Also updates VerifyReadOnlyPointers to check that RO_SPACE objects' maps are
also in RO_SPACE. Previously the invariant did not hold for Strings which still
had their maps in MAP_SPACE.

Also moves invalid_prototype_validity_cell to RO_SPACE.

    RO_SPACE  NEW_SPACE  OLD_SPACE  CODE_SPACE  MAP_SPACE  LO_SPACE
old    22024          0     229184       32928       8184         0
new    31488          0     229184       32928        176         0

Bug: v8:7464
Change-Id: I870d22cc5234ba60b3ef8a2ada590ee6ae426c9f
Reviewed-on: https://chromium-review.googlesource.com/1013494Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52848}