Port dfdcaf43
Port 2e1f5567

Original Commit Message:

    This CL introduces TurboAssembler, a super-class of Assembler and sub-class
    of MacroAssembler. TurboAssembler contains all the functionality that is used
    by Turbofan and previously was part of MacroAssembler. TurboAssembler has
    access to the isolate but, in contrast to MacroAssembler, does not expect to
    be running on the main thread.

R=neis@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:6048
LOG=N

Change-Id: I3f51771afefe46410db7cda2625472d78c87f8c6
Reviewed-on: https://chromium-review.googlesource.com/583584Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Jaideep Bajwa <bjaideep@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#46900}