[heap] Reland "Cancel tasks before tearing down the heap."

src/cancelable-task.h

Index: src/cancelable-task.h
diff --git a/src/cancelable-task.h b/src/cancelable-task.h
index b1d62aad4bd595428d0b73da7497b67bca15a712..8e05cb696e5e7e061b0c12f8fd5b1463d5f16ec0 100644
--- a/src/cancelable-task.h
+++ b/src/cancelable-task.h
@@ -27,6 +27,7 @@ class CancelableTaskManager {
 
   // Registers a new cancelable {task}. Returns the unique {id} of the task that
   // can be used to try to abort a task by calling {Abort}.
+  // Should not be called after CancelAndWait.

[Michael Lippautz, 2016/10/14 09:29:20]

s/Should/Must/

(since it's a CHECK now)

[ulan, 2016/10/14 09:34:35]

Done.

   uint32_t Register(Cancelable* task);
 
   // Try to abort running a task identified by {id}. The possible outcomes are:
@@ -59,6 +60,8 @@ class CancelableTaskManager {
   base::ConditionVariable cancelable_tasks_barrier_;
   base::Mutex mutex_;
 
+  bool canceled_;
+
   friend class Cancelable;
 
   DISALLOW_COPY_AND_ASSIGN(CancelableTaskManager);