libstdc++: fix incomplete type for FramebufferCache libstdc++ does not allow incomplete type for T2 with std::pair<T1,T2> and fails with: .../../src/libANGLE/renderer/vulkan/vk_cache_utils.h:1570:64: required from here /usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/include/g++-v9/bits/stl_pair.h:215:11: error: std::pair<_T1, _T2>::second has incomplete type 215 | _T2 second; /// @c second is a copy of the second object | ^~~~~~ https://chromium-review.googlesource.com/c/angle/angle/+/2580111 added class FramebufferCache with incomplete type in |mPayload| to vk::FramebufferHelper. Changing include order is not an option. However, FramebufferCache is only used in FramebufferVk and we can make it local there. Bug: chromium:957519 Change-Id: I5fbdca23adbb9f4aecc266988c02fb0d051504cb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2621473 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>