More source position improvements and tests

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index afbc9b2cc1b76a4c7c34e769d89620ff82dccbdc..bc01c87c03f2d6ccbc719bc3efa59500a481a49d 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -43,7 +43,8 @@ class UnboxIntegerInstr;
 #define CLASSIFYING_TOKEN_POSITIONS(V)                                         \
     V(Box, -2)                                                                 \
     V(ParallelMove, -3)                                                        \
-    V(TempMove, -4)
+    V(TempMove, -4)                                                            \
+    V(Constant, -5)
 
 // COMPILE_ASSERT that all CLASSIFYING_TOKEN_POSITIONS are less than
 // Scanner::kNoSourcePos.
@@ -2582,7 +2583,7 @@ class ConstraintInstr : public TemplateDefinition<1, NoThrow> {
 class ConstantInstr : public TemplateDefinition<0, NoThrow, Pure> {
  public:
   ConstantInstr(const Object& value,
-                intptr_t token_pos = Scanner::kNoSourcePos);
+                intptr_t token_pos = ClassifyingTokenPositions::kConstant);
 
   DECLARE_INSTRUCTION(Constant)
   virtual CompileType ComputeType() const;
@@ -2599,6 +2600,8 @@ class ConstantInstr : public TemplateDefinition<0, NoThrow, Pure> {
 
   virtual bool AttributesEqual(Instruction* other) const;
 
+  virtual intptr_t token_pos() const { return token_pos_; }
+
  private:
   const Object& value_;
   const intptr_t token_pos_;