When == is invoked on a Symbol or SIMD vector and an object, the object should
be converted to a primitive with ToPrimitive and then compared again. This means,
for example, that for a Symbol or SIMD vector s, s == Object(s). This patch makes
that change in the implementation of ==. Only the runtime function needed to be
changed, as the code stubs and compiler specializations don't operate on Symbols
or SIMD vectors, and on these types, a fallback to the runtime function is always
used.

BUG=v8:3593
LOG=Y
R=adamk

Review URL: https://codereview.chromium.org/1421413002

Cr-Commit-Position: refs/heads/master@{#31614}