port 7015fd20 (r29402)

original commit message:

    Up until now the context register was listed explicitly in each stub's
    CallInterfaceDescriptor. This was problematic, because it was listed
    first in the list of register parameters--which is fine for Crankshaft,
    which is more or less built to handle the context as the first
    parameter-- but not ideal for TurboFan, which adds the context at
    the end of all function parameters. Now the context register is no
    longer in the register list and can be handled appropriately by both
    compilers. Specifically, this allows the FunctionType specified for
    each CallInterfaceDescriptor to exactly match the parameter register
    list.

BUG=

Review URL: https://codereview.chromium.org/1216543004

Cr-Commit-Position: refs/heads/master@{#29433}