Reason for revert:

   original commit was reverted.

   This reverts commit c3529ce5.

   original issues's description:

   > X87: Resolve references to "this" the same way as normal variables
   >
   > port 06a792b7 (r28263).
   >
   > original commit message:
   >
   >  Make the parser handle references to "this" as unresolved variables, so the
   >  same logic as for the rest of function parameters is used for the receiver.
   >  Minor additions to the code generation handle copying the receiver to the
   >  context, along with the rest of the function parameters.
   >
   >  Based on work by Adrian Perez de Castro <aperez@igalia.com>

BUG=

Review URL: https://codereview.chromium.org/1130913005

Cr-Commit-Position: refs/heads/master@{#28307}