Perhaps you could in an MVP implementation, but in practice no, none of the serious implementations do that by default. First because native OpenGL drivers are generally a mess, so browsers actually implement WebGL on top of DirectX, Vulkan or Metal wherever they can, and even when those aren't available the browsers still parse, validate and reconstitute the GLSL rather than passing it straight through to OpenGL as a layer of insulation against driver bugs. Chrome and Firefox do have hidden feature flags which bypass that behavior and call the native GL implementation directly, but you probably shouldn't enable those unless you're really into ShaderToy and want it to compile faster.