[gin] Make Converter<std::vector<T>> return v8::Local if Converter<T> does.

For consistency between the methods, have all converters take v8::Isolate*,
as all of the ones that presently take v8::Local<v8::Context> implicitly
assume it to be the current context anyhow.

Bug: None
Change-Id: I565fb54bdc7a1d5ac1796ef5d7c1c69ca83290bb
Reviewed-on: https://chromium-review.googlesource.com/876563
Commit-Queue: Jeremy Roman <[email protected]>
Reviewed-by: Devlin <[email protected]>
Cr-Commit-Position: refs/heads/master@{#532473}
7 files changed