[turbofan] Add DebugBreak machine operator and support

src/compiler/code-assembler.h

 // Copyright 2015 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.
 
 #ifndef V8_COMPILER_CODE_ASSEMBLER_H_
 #define V8_COMPILER_CODE_ASSEMBLER_H_
 
 #include <map>
 
 // Clients of this interface shouldn't depend on lots of compiler internals.
@@ skipping 191 matching lines @@
 
   Node* Parameter(int value);
   void Return(Node* value);
 
   void Bind(Label* label);
   void Goto(Label* label);
   void GotoIf(Node* condition, Label* true_label);
   void GotoUnless(Node* condition, Label* false_label);
   void Branch(Node* condition, Label* true_label, Label* false_label);
 
+  void DebugBreak();

[Michael Starzinger, 2016/05/19 08:53:23]

nit: Can we move this up or down a few lines? Right now it sits right in between
the control flow operators (i.e. between Branch and Switch). How about line 205
instead?

[danno, 2016/05/19 09:05:04]

Done.

+
   void Switch(Node* index, Label* default_label, int32_t* case_values,
               Label** case_labels, size_t case_count);
 
   // Access to the frame pointer
   Node* LoadFramePointer();
   Node* LoadParentFramePointer();
 
   // Access to the stack pointer
   Node* LoadStackPointer();
 
@@ skipping 172 matching lines @@
   // Map of variables to the list of value nodes that have been added from each
   // merge path in their order of merging.
   std::map<Variable::Impl*, std::vector<Node*>> variable_merges_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CODE_ASSEMBLER_H_