Fix ASAN bug caused by passing empty label string. This CL will fix the ASAN bug that was caused by passing empty label string to getMultisampledRenderTarget, function of TextureStorage11. Instead, pass mTextureLabel so we can get WebGL labels now. Also to avoid this in future, convert ref mTextureLabel to now store copy. The change in the test reflects the steps to first set the label string and later the label being used to initialize mTextureLabel via texture storage creation. Bug: chromium:1254746 Change-Id: I007bdf1c7a421a2b4b9288aa71fa4368c14cf333 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3201030 Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Rafael Cintron <rafael.cintron@microsoft.com>