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

src/full-codegen/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/ast/scopes.h"
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
@@ skipping 1078 matching lines @@
   // permanent slow case into register rdx.
   __ movp(rdx, Operand(rsp, 3 * kPointerSize));
 
   // Check if the expected map still matches that of the enumerable.
   // If not, we may have to filter the key.
   Label update_each;
   __ movp(rcx, Operand(rsp, 4 * kPointerSize));
   __ cmpp(rdx, FieldOperand(rcx, HeapObject::kMapOffset));
   __ j(equal, &update_each, Label::kNear);
 
-  // For proxies, no filtering is done.
-  // TODO(rossberg): What if only a prototype is a proxy? Not specified yet.
-  __ Cmp(rdx, Smi::FromInt(0));
-  __ j(equal, &update_each, Label::kNear);
-
   // Convert the entry to a string or null if it isn't a property
   // anymore. If the property has been removed while iterating, we
   // just skip it.
   __ Push(rcx);  // Enumerable.
   __ Push(rbx);  // Current entry.
   __ CallRuntime(Runtime::kForInFilter, 2);
   PrepareForBailoutForId(stmt->FilterId(), TOS_REG);
   __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
   __ j(equal, loop_statement.continue_label());
   __ movp(rbx, rax);
@@ skipping 3717 matching lines @@
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64