Handle infinite length during normalizing a vector.

[BorisChiou]

Rotate3d may use some extremely large value in the rotate axis vector, and
this may cause infinite length, so the normalized vector becomes a zero vector.
Here, we scale the vector first if its length is infinite, and then do the normalization.

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This change is 

[BorisChiou]

@nical could you please review this? Bug 1467277 needs this patch to generate a correct rotate transform matrix in some special cases.

[BorisChiou]

I'm not sure the workflow if I'd like to update euclid and gecko, so I guess I need to create this PR, and then update servo/components/style/Cargo.toml, and then revender rust (or say bump the version?) in Gecko side.

[nical]

Nice cacth! normalize is used in a lot of places and often enough we are confident that the range of values don't require the extra code, so I'd prefer to opt into the robustness here. Would you mind adding another method robust_normalize(self) -> T instead?

For updates I am not sure about the specifics of the style system, but since your PR doesn't introduce a breaking change, I think that all we need is to:

• make changes to euclid on this repo
• publish euclid on crates.io
• update the Cargo.toml of that part that needs this change
• in mozilla-central, go to toolkit/library/rust and run cargo update -p euclid
• run the same cargo update command in toolkit/library/gtest/rust
• run mach vendor rust at the root of mozilla-central.

When there is a breaking change we first need to go through all of the gecko crates that depend on euclid and update their version of euclid before we can do the steps above, which is a bit of a pain.

[BorisChiou]

Cool! OK, let's add another method, robust_normalize(self) -> T. Thanks for the instructions.

[BorisChiou]

I updated this. @nical, couold you please check again? Thanks for the help.

[nical]

Neat! @bors-servo r+

[bors-servo]

📌 Commit 6406807 has been approved by nical

[bors-servo]

⌛ Testing commit 6406807 with merge 4c254dc...

[bors-servo]

☀️ Test successful - status-travis
Approved by: nical
Pushing 4c254dc to master...