port 8016547c (r30818).

original commit message:

    The StringCompareStub used to take its parameters on the (JavaScript)
    stack, which made it impossible to use in TurboFan. Actually
    StringCompareStub was currently completely unused. This changes the
    calling convention to something TurboFan compatible and introduces a
    CallInterfaceDescriptor for StringCompareStub. It also changes
    HStringCompareAndBranch to use the StringCompareStub instead of using
    the full blown CompareICStub for a stupid string comparison.

BUG=

Review URL: https://codereview.chromium.org/1355983003

Cr-Commit-Position: refs/heads/master@{#30845}