[win32] Fix overflow in TaskRunnerWindow.

[knopp]

Fixes #182501

Right now empty TaskRunner::ProcessTasks() returns TaskTimePoint::max() - now (relative time). This causes problems, because the value is later used in TaskRunnerWindow to schedule timer at std::chrono::high_resolution_clock::now() + relative_time). This of course overflows, because the new now() in TaskRunnerWindow is higher than the value used to calculate original delta inside TaskRunner.

TaskRunnerWindow already had special case where it checks for std::chrono::nanoseconds::max(). In this PR the behavior of TaskRunnerWindow::SetTimer has been updated to check for overflow rather than excepcting a special value.

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Code Review

This pull request modifies TaskRunner::ProcessTasks() to return std::chrono::nanoseconds::max() when its task queue is empty. This change prevents a potential overflow issue in TaskRunnerWindow which could occur when calculating the next timer schedule from the previously returned relative time. A new unit test is added to confirm that ProcessTasks returns std::chrono::nanoseconds::max() for an empty task runner.

[loic-sharma]

Thanks for fixing this!

[loic-sharma]

Cherrypick is here: #182864