[proxy] fixing harmony/proxy.js tests and improving error messages + some drive-by fixes

src/full-codegen/arm/full-codegen-arm.cc

Index: src/full-codegen/arm/full-codegen-arm.cc
diff --git a/src/full-codegen/arm/full-codegen-arm.cc b/src/full-codegen/arm/full-codegen-arm.cc
index acd877f62b3e79a30775456ab940d385ca94509a..5e8afbfd0a66451321e15f9e0b8255f73f56bf26 100644
--- a/src/full-codegen/arm/full-codegen-arm.cc
+++ b/src/full-codegen/arm/full-codegen-arm.cc
@@ -1146,11 +1146,6 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   __ cmp(r4, Operand(r2));
   __ b(eq, &update_each);
 
-  // For proxies, no filtering is done.
-  // TODO(rossberg): What if only a prototype is a proxy? Not specified yet.
-  __ cmp(r2, Operand(Smi::FromInt(0)));
-  __ b(eq, &update_each);
-
   // Convert the entry to a string or (smi) 0 if it isn't a property
   // any more. If the property has been removed while iterating, we
   // just skip it.