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This affects the generated code of the constructor, which will now throw
a TypeError if "parameter 1 is not of type 'Path2D'."

However, this code path is unreachable, because there's a type check
(V8Path2D::hasInstance()) to determine that this form of the constructor
should be used.

Promoting [TypeChecking=Interface] to the interface level will make it
possible to make [TypeChecking=Interface] the default without changing
the generated code for this interface.

BUG=462561

Review URL: https://codereview.chromium.org/1471563002

Cr-Commit-Position: refs/heads/master@{#361317}