Apple and Mozilla were the first to have prototypes (one "inspired" by Metal, the other by Vulkan), both looked quite different from the final WebGPU spec though.
This isn’t correct. All 3 parties had prototypes. Mozilla’s first prototype was based on Metal and implemented in Servo. Then we (Mozilla) proposed a Vulkan-like API and had another WIP in Servo, but it was also thrown out.
On January 24, 2017, Khronos hosted an IP-free meeting dedicated to discussion of "WebGL Next" ideas, collided with WebGL working group meeting in Vancouver.[8] Google team presented the NXT prototype implementing a new API that could run in Chromium with OpenGL, or standalone with OpenGL and Metal. NXT borrowed concepts from all of Vulkan, Direct3D 12, and Metal native APIs. Apple and Mozilla representatives also showed their prototypes built on Safari and Servo correspondingly, both of which closely replicated the Metal API
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(Note: Unlike Chrome, Apple and Mozilla followed the actual standards route: two independent implementations)
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On February 7, 2017, Apple's WebKit team proposed the creation of the W3C community group to design the API. At the same time they announced a technical proof of concept and proposal under the name "WebGPU", based on concepts in Apple's Metal.
Apple is literally at the forefront of this entire initiative with Mozilla close second. Chrome grudgingly agreed to join the others a full year later.
