Add new style of string interpolation optimization: new nodes, working constant folding.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 28731)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -302,6 +302,9 @@
   // Create non-nullable Int type.
   static CompileType Int();
 
+  // Create non-nullable String type.
+  static CompileType String();
+
   // Perform a join operation over the type lattice.
   void Union(CompileType* other);
 
@@ -650,6 +653,7 @@
   M(CheckArrayBound)                                                           \
   M(Constraint)                                                                \
   M(StringFromCharCode)                                                        \
+  M(StringInterpolate)                                                         \
   M(InvokeMathCFunction)                                                       \
   M(GuardField)                                                                \
   M(IfThenElse)                                                                \
@@ -3649,6 +3653,34 @@
 };
 
 
+class StringInterpolateInstr : public TemplateDefinition<1> {
+ public:
+  StringInterpolateInstr(Value* value, intptr_t token_pos)
+      : token_pos_(token_pos), function_(Function::Handle()) {
+    SetInputAt(0, value);
+  }
+
+  Value* value() const { return inputs_[0]; }
+  intptr_t token_pos() const { return token_pos_; }
+
+  virtual CompileType ComputeType() const;
+  // Issues a static call to Dart code whihc calls toString on objects.
+  virtual EffectSet Effects() const { return EffectSet::All(); }
+  virtual bool CanDeoptimize() const { return true; }
+  virtual bool MayThrow() const { return true; }
+
+  const Function& CallFunction() const;
+
+  DECLARE_INSTRUCTION(StringInterpolate)
+
+ private:
+  const intptr_t token_pos_;
+  Function& function_;
+
+  DISALLOW_COPY_AND_ASSIGN(StringInterpolateInstr);
+};
+
+
 class StoreIndexedInstr : public TemplateDefinition<3> {
  public:
   StoreIndexedInstr(Value* array,