Hydrogen LoopBuilder: add support for "while(true) {...}" loops

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index a0fdf00f9d706cc58dda92ca9573aa50e72a98ff..84d69ca755259acea6972630ef04c91ecf54dc4c 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -1669,9 +1669,11 @@ class HGraphBuilder {
       kPreIncrement,
       kPostIncrement,
       kPreDecrement,
-      kPostDecrement
+      kPostDecrement,
+      kWhileTrue
     };
 
+    explicit LoopBuilder(HGraphBuilder* builder);  // while (true) {...}
     LoopBuilder(HGraphBuilder* builder,
                 HValue* context,
                 Direction direction);
@@ -1689,11 +1691,15 @@ class HGraphBuilder {
         HValue* terminating,
         Token::Value token);
 
+    void BeginBody(int drop_count);
+
     void Break();
 
     void EndBody();
 
    private:
+    void Initialize(HGraphBuilder* builder, HValue* context,
+                    Direction direction, HValue* increment_amount);
     Zone* zone() { return builder_->zone(); }
 
     HGraphBuilder* builder_;