This patch implements buffer lazy initialization before writeBuffer():
if the buffer is not initialized and writeBuffer() doesn't cover the
whole buffer, the buffer will be cleared to 0, otherwise the buffer
shouldn't be cleared.
This patch also introduces a toggle LazyClearBufferOnFirstUse for the
development of buffer lazy initialization: before buffer lazy
initialization being completely supported, all the related code will
only be enabled behind this toggle to prevent the buffers with valid
content being unexpectedly cleared.
BUG=dawn:414
TEST=dawn_end2end_tests
Change-Id: I99a2aa98ca4b9b21d69c6b32080afb525e2c4ad3
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/24041
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
