commit e66c94540942da7827d7c68c317e85aeaddccda8
author Maksim Ivanov <emaxx@chromium.org> Thu Sep 03 15:22:16 2020
committer Commit Bot <commit-bot@chromium.org> Thu Sep 03 15:22:16 2020
tree a0d00f4aea713cb959821079e9a9e3f13972c4d2
parent 8ea2f21432cb37cb23a3370643dd596a283ce01a

Hint BrowserTaskEnvironment in task API failures

Print developer-friendly DCHECK failure messages in case the program
crashes due to misuse of Task APIs - e.g., trying to post a task to the
UI thread in a unit test without creating a BrowserTaskEnvironment.

This targets these two (mis)usage scenarios:
(1) calling content::GetUIThreadTaskRunner()/GetIOThreadTaskRunner()
    without having a BrowserTaskEnvironment;
(2) calling base::PostTask() with |content::BrowserThread::UI|/|::IO|
    without having a BrowserTaskEnvironment.

Before this change, these scenarios were triggering obscure crashes that
are hard to decipher for developers, namely:
* "[FATAL:browser_task_executor.cc(293)] Check failed:
  g_browser_task_executor." for scenario #1;
* "[FATAL:task_executor.cc(70)] Check failed: executor." for scenario #2.

In order to improve this, the following changes were made:

* A DCHECK message was added into
  base::GetRegisteredTaskExecutorForTraits() - the previous
  message-less DCHECK was preventing the helpful message in
  base::GetTaskExecutorForTraits()'s DCHECK from being reached.
  This helps in the scenario #2 from above.

* A DCHECK message was added into BrowserTaskExecutor::Get() that is
  analogous to the DCHECK message from base::GetTaskExecutorForTraits(),
  and code throughout the file was changed to use this Get() function
  instead of DCHECK'ing the same without any message.
  This helps in the scenario #1 from above.

* A Death unit test was added that verifies that scenarios #1 and #2
  trigger DCHECK failures that contain the "BrowserTaskEnvironment"
  substring, which would prevent from regressing in this debug logging
  again.

Bug: none
Change-Id: I959c4971537d2096321e573d148974f347a58f5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368600
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804238}