Implement document load cancellation
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"./mach env" cause unclear message.
We did't use "LD_LIBRARY_PATH" and no need display this.
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Remove the print message.
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Adjust import path for WPT tests to accommodate upstream.
This should avoid the ongoing issues where new dependencies are vendored upstream and our setup throws exceptions when some code tries to import them.
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If we have a rotate axis whose length is extremely large, we will get an
infinite value, and its normalized vector is a zero vector, instead of an
unit vector, i.e. (x/inf, y/inf, z/inf) == (0, 0, 0).
The solution is: we scale the vector, so the length becomes a finite value, and
we could get a valid unit vector.
Therefore, we use a different normalization method, robust_normalize().
Bug: 1467277
Reviewed-by: hiro
