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This CL makes GPUDevice an EventTarget. When an uncaptured error is
raised in Dawn, the "uncapturederror" error is fired in GPUDevice.

Change-Id: Ib0082e080667448e309d9879ea22de7ac1706fad
Bug: 877147
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787504
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694216}