[turbofan] Add some documenting comments to RawMachineAssembler.

src/compiler/raw-machine-assembler.cc

 // Copyright 2014 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.
 
 #include "src/code-factory.h"
 #include "src/compiler/pipeline.h"
 #include "src/compiler/raw-machine-assembler.h"
 #include "src/compiler/scheduler.h"
 
 namespace v8 {
@@ skipping 21 matching lines @@
     parameters_[i] =
         NewNode(common()->Parameter(static_cast<int>(i)), graph->start());
   }
 }
 
 
 Schedule* RawMachineAssembler::Export() {
   // Compute the correct codegen order.
   DCHECK(schedule_->rpo_order()->empty());
   Scheduler::ComputeSpecialRPO(zone(), schedule_);
-  // Invalidate MachineAssembler.
+  // Invalidate RawMachineAssembler.
   Schedule* schedule = schedule_;
   schedule_ = NULL;
   return schedule;
 }
 
 
 Node* RawMachineAssembler::Parameter(size_t index) {
   DCHECK(index < parameter_count());
   return parameters_[index];
 }
@@ skipping 183 matching lines @@
 
 
 BasicBlock* RawMachineAssembler::CurrentBlock() {
   DCHECK(current_block_);
   return current_block_;
 }
 
 
 Node* RawMachineAssembler::MakeNode(const Operator* op, int input_count,
                                     Node** inputs) {
-  DCHECK(ScheduleValid());
+  DCHECK_NOT_NULL(schedule_);
   DCHECK(current_block_ != NULL);
   Node* node = graph()->NewNode(op, input_count, inputs);
   BasicBlock* block = op->opcode() == IrOpcode::kParameter ? schedule()->start()
                                                            : CurrentBlock();
   if (op->opcode() != IrOpcode::kReturn) {
     schedule()->AddNode(block, node);
   }
   return node;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8