This is a reland of f8ae62fe

Original change's description:
> [heap] Move initial objects into RO_SPACE
> 
> This moves:
> * the main oddballs (null, undefined, hole, true, false) as well as
> their supporting maps (also adds hole as an internalized string to make
> this work).
> * most of the internalized strings
> * the struct maps
> * empty array
> * empty enum cache
> * the contents of the initial string table
> * the weak_cell_cache for any map in RO_SPACE (and eagerly creates the
> value avoid writing to it during run-time)
> 
> The StartupSerializer stats change as follows:
> 
>      RO_SPACE  NEW_SPACE  OLD_SPACE  CODE_SPACE  MAP_SPACE  LO_SPACE
> old         0          0     270264       32608      12144         0
> new     21776          0     253168       32608       8184         0
> Overall memory usage has increased by 720 bytes due to the eager
> initialization of the Map weak cell caches.
> 
> Also extends --serialization-statistics to print out separate instance
> type stats for objects in RO_SPACE as shown here:
> 
>   Read Only Instance types (count and bytes):
>        404      16736  ONE_BYTE_INTERNALIZED_STRING_TYPE
>          2         32  HEAP_NUMBER_TYPE
>          5        240  ODDBALL_TYPE
>         45       3960  MAP_TYPE
>          1         16  BYTE_ARRAY_TYPE
>          1         24  TUPLE2_TYPE
>          1         16  FIXED_ARRAY_TYPE
>          1         32  DESCRIPTOR_ARRAY_TYPE
>         45        720  WEAK_CELL_TYPE
> 
> Bug: v8:7464
> Change-Id: I12981c39c82a7057f68bbbe03f89fb57b0b4c6a6
> Reviewed-on: https://chromium-review.googlesource.com/973722
> Commit-Queue: Dan Elphick <delphick@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52435}

Bug: v8:7464
Change-Id: I50427edfeb53ca80ec4cf46566368fb2213ccf7b
Reviewed-on: https://chromium-review.googlesource.com/999654
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52638}