Simplify AST ID generation.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index c75938e22d8689010a630ddbfd804a6093d59384..a5c7cb145a408876a7f8b8f0eb75f91b1e7c7533 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -184,7 +184,7 @@ class AstNode: public ZoneObject {
   // For generating IDs for AstNodes.
   class IdGen {
    public:
-    explicit IdGen(int id = 0) : id_(id) {}
+    IdGen() : id_(BailoutId::FirstUsable().ToInt()) {}

[wingo, 2014/10/08 13:34:46]

What is the plan with bailout ids -- still a per-function locally unique
incrementing integer?  For parameter destructuring of arrow functions I will
have to transplant expressions from one function to another.  I'm finally
starting on that now:
https://docs.google.com/document/d/1iJWvuakeKsPJOeA-RJ-4bM3Jha5iewQjxKsylgzHE....
 The plan was to see if we could add a post-pass to assign bailout ids, to see
how that would impact perf, because when transplanting you have to preserve
local uniqueness; but is that still a valid strategy?

 
     int GetNextId() { return ReserveIdRange(1); }
     int ReserveIdRange(int n) {
@@ -195,6 +195,8 @@ class AstNode: public ZoneObject {
 
    private:
     int id_;
+
+    DISALLOW_COPY_AND_ASSIGN(IdGen);
   };
 
 #define DECLARE_TYPE_ENUM(type) k##type,