WIP [esnext] implement async iteration proposal

src/compiler/machine-graph-verifier.cc

Index: src/compiler/machine-graph-verifier.cc
diff --git a/src/compiler/machine-graph-verifier.cc b/src/compiler/machine-graph-verifier.cc
index ecabbe057530b6eaec020dbe1ff4dd479ee9fcf1..cf2e92244bd769ce5ff980937d6a70e9fd41061f 100644
--- a/src/compiler/machine-graph-verifier.cc
+++ b/src/compiler/machine-graph-verifier.cc
@@ -519,6 +519,8 @@ class MachineRepresentationChecker {
           case IrOpcode::kTypedStateValues:
           case IrOpcode::kFrameState:
             break;
+          case IrOpcode::kRetain:

[caitp, 2017/01/10 04:13:41]

TODO(caitp): get rid of this (and any calls to Retain() added in CSA builtins in
this patch, they didn't really solve any GC issues I was debugging previously)

+            break;
           default:
             if (node->op()->ValueInputCount() != 0) {
               std::stringstream str;