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

src/full-codegen/mips/full-codegen-mips.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_MIPS
 
 // Note on Mips implementation:
 //
 // The result_register() for mips is the 'v0' register, which is defined
 // by the ABI to contain function return values. However, the first
@@ skipping 1120 matching lines @@
   // permanent slow case into register a2.
   __ lw(a2, MemOperand(sp, 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;
   __ lw(a1, MemOperand(sp, 4 * kPointerSize));
   __ lw(t0, FieldMemOperand(a1, HeapObject::kMapOffset));
   __ Branch(&update_each, eq, t0, Operand(a2));
 
-  // For proxies, no filtering is done.
-  // TODO(rossberg): What if only a prototype is a proxy? Not specified yet.
-  DCHECK_EQ(static_cast<Smi*>(0), Smi::FromInt(0));
-  __ Branch(&update_each, eq, a2, Operand(zero_reg));
-
   // 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.
   __ Push(a1, a3);  // Enumerable and current entry.
   __ CallRuntime(Runtime::kForInFilter, 2);
   PrepareForBailoutForId(stmt->FilterId(), TOS_REG);
   __ mov(a3, result_register());
   __ LoadRoot(at, Heap::kUndefinedValueRootIndex);
   __ Branch(loop_statement.continue_label(), eq, a3, Operand(at));
 
@@ skipping 3757 matching lines @@
          reinterpret_cast<uint32_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS