Add GC-friendly replacement for default Map/Set:
* open-addressing hash table, avoiding the overhead of chained entries
* index separate from the keys/values, allowing more of it to fit in the cache
* new keys are always appended, to allow insertion-order iteration
* spare bits in index entries are used to store hashes
* index is typed data, so can be ignored by GC
Enable it with --use_compact_hash (disabled by default).
Reduces Dart2JS compilation time for huge codebase (N=200) by ~30%, due to reduced time in GC. Slightly slower for small maps and maps with deletions: json benchmarks regress by ~5%.
R=vegorov@google.com
Review URL: https://codereview.chromium.org//915323002
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@43840 260f80e4-7a28-3924-810f-c04153c831b5
koda@google.com