Detailed report: https://clusterfuzz.com/testcase?key=5699126574579712

Fuzzer: metzman_webgl_mutator
Job Type: linux_ubsan_vptr_chrome
Platform Id: linux

Crash Type: Null-dereference READ
Crash Address: 0x000000000000
Crash State:
  tcmalloc::PageHeap::MergeIntoFreeList
  tcmalloc::PageHeap::Delete
  tcmalloc::CentralFreeList::ReleaseToSpans
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=linux_ubsan_vptr_chrome&range=508470:508498

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5699126574579712

Issue filed automatically.

See https://github.com/google/clusterfuzz-tools for instructions to reproduce this bug locally.