Correct static_asserts in VectorTraits.h
Correct static_asserts in VectorTraits.h

The current static_asserts are not correct.

- canInitializeWithMemset should check IsTriviallyDefaultConstructible<T>::value
- canMoveWithMemcpy should check IsTriviallyMoveAssignable<T>::value
- canCompareWithMemcmp should check IsScalar<T>::value

BUG=475801

Review URL: https://codereview.chromium.org/1104633002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@194353 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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