Include <chrono> for high_resolution_clock

[StephanTLavavej]

I work on Microsoft Visual C++, where we regularly build popular open-source projects, including yours, with development builds of our compiler and libraries to detect and prevent shipping regressions that would affect you. This also allows us to provide advance notice of breaking changes, which is the case here.

I just merged microsoft/STL#5105, which revealed a conformance issue in cppcoro.

Compiler error with this STL change:

C:\gitP\andreasbuhr\cppcoro\test\cancellation_token_tests.cpp(294,28): error C3083: 'high_resolution_clock': the symbol to the left of a '::' must be a type

Affected code:

cppcoro/test/cancellation_token_tests.cpp

Line 294 in a4ef652

auto start = std::chrono::high_resolution_clock::now();

This was assuming that including <thread> makes the chrono::high_resolution_clock type available, which is not guaranteed by the Standard. You must explicitly include <chrono>.

[andreasbuhr]

Thanks a lot