Ensure Freed TLS Slots Contain nullptr on Reallocation

Code generally depends on TLS slots initialized to zero. This means
that code that gets a reused slot also depends on the reused slot
containing zero.

This CL introduces a versioning system to allow us to quickly determine
if a slot was previously freed.

Also added overview comments as a bonus.

BUG=590907

Review-Url: https://codereview.chromium.org/2383833004
Cr-Commit-Position: refs/heads/master@{#423952}


CrOS-Libchrome-Original-Commit: c90ffe2a6c10bb34c8eed5225f6d3e4d3be23acb
3 files changed
tree: 36c78d8879f6e66836fffbdb68b230d98dcc91ac
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/