There's a longstanding TODO in ValidateSubSourceAndGetData about changing the outgoing "long long" argument to GLuint.

https://cs.chromium.org/chromium/src/third_party/blink/renderer/modules/webgl/webgl2_rendering_context_base.cc?type=cs&q=ValidateSubSourceAndGetData&sq=package:chromium&g=0&l=45

This came up again in the context of Issue 879657. After the cleanup in https://chromium-review.googlesource.com/1398786 lands, we should make this change and remove some of the static_casts.