Improve positions tracking inside the HGraphBuilder.

src/compiler.h

Index: src/compiler.h
diff --git a/src/compiler.h b/src/compiler.h
index 9d1baa3280590e7e4d2905c951710ca61f444a50..f7ff09c57d74e7678c4873e347d5baa17b77ba7d 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -227,6 +227,7 @@ class CompilationInfo {
     SetMode(OPTIMIZE);
     osr_ast_id_ = osr_ast_id;
     unoptimized_code_ = unoptimized;
+    optimization_id_ = isolate()->NextOptimizationId();
   }
   void DisableOptimization();
 
@@ -315,6 +316,8 @@ class CompilationInfo {
     return osr_ast_id_ == osr_ast_id && function.is_identical_to(closure_);
   }
 
+  int optimization_id() const { return optimization_id_; }
+
  protected:
   CompilationInfo(Handle<Script> script,
                   Zone* zone);
@@ -450,6 +453,8 @@ class CompilationInfo {
 
   Handle<Foreign> object_wrapper_;
 
+  int optimization_id_;
+
   DISALLOW_COPY_AND_ASSIGN(CompilationInfo);
 };