WindowTreeHostPlatform::OnAcceleratedWidgetAvailable() ignores device_pixel_ratio parameter. WindowTreeHost always initializes device_pixel_ratio as DPI of the display, see https://codesearch.chromium.org/chromium/src/ui/aura/window_tree_host.cc?type=cs&sq=package:chromium&g=0&l=104 . 
This is problematic on Fuchsia where there is no API to get device_pixel_ratio for a display. It's reported as a view property.