Initial steps towards cleaning up integer arithmetic IR.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 7fcebdb0f57465048ce8f64e7cd51388ed40e82f..16abb50ee86cc31ed0f2ccb2c144926e02cdaaed 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -5145,6 +5145,9 @@ class Integer : public Number {
 
   virtual double AsDoubleValue() const;
   virtual int64_t AsInt64Value() const;
+  virtual int64_t AsTruncatedInt64Value() const {
+    return AsInt64Value();
+  }
   virtual uint32_t AsTruncatedUint32Value() const;
 
   virtual bool FitsIntoSmi() const;
@@ -5310,6 +5313,7 @@ class Bigint : public Integer {
 
   virtual double AsDoubleValue() const;
   virtual int64_t AsInt64Value() const;
+  virtual int64_t AsTruncatedInt64Value() const;
   virtual uint32_t AsTruncatedUint32Value() const;
 
   virtual int CompareWith(const Integer& other) const;