The bug 670596 allows to reclaim the unused memory inside GC chunks. With this change it would not be problematic to have huge GC chunks that are significantly bigger than the current 1MB limit. On the other hand, with such huge chunks on 32-bits we can run out of the virtual address space with multiple JS runtimes allocated for web workers. In addition, the initialization cost for a huge chunk that match the size of a typical browser session is non-trivial. This suggests to support dynamically-sized chunks with small initial size that grows as necessary.