BUG=angleproject:1002 A 'LoadFunction' is used to load data of a given <GL format, GL type> pair into a specific DXGI_FORMAT. Before this change, BuildD3D11LoadFunctionMap mapped <GL format, GL type> pairs to LoadFunctions. This meant each <GL format, GL type> pair could only loaded using one LoadFunction, and therefore could only be loaded into one specific DXGI_FORMAT. We now want to map <GL format, GL type, DXGI_FORMAT> triples to LoadFunctions. This allows us to use different DXGI_FORMATS for each <GL format, GL type> pair, depending on the capabilities of the underlying D3D11 device. Change-Id: I3b5e24c4bf98f18360ddd45b2022a90b5000f866 Reviewed-on: https://chromium-review.googlesource.com/270561Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Austin Kinross <aukinros@microsoft.com>