Canonicalize all integer constants taht we create by parsing a string.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 15426)
+++ runtime/vm/object.h	(working copy)
@@ -3465,6 +3465,10 @@
 class Integer : public Number {
  public:
   static RawInteger* New(const String& str, Heap::Space space = Heap::kNew);
+
+  // Returns a canonical Integer object allocated in the old gen space.
+  static RawInteger* NewCanonical(const String& str);
+
   static RawInteger* New(int64_t value, Heap::Space space = Heap::kNew);
 
   virtual double AsDoubleValue() const;
@@ -3623,6 +3627,9 @@
 
   static RawBigint* New(const String& str, Heap::Space space = Heap::kNew);
 
+  // Returns a canonical Bigint object allocated in the old gen space.
+  static RawBigint* NewCanonical(const String& str);
+
   RawBigint* ArithmeticOp(Token::Kind operation, const Bigint& other) const;
 
  private: