Reapply CL "Option to truncate integers to 64 bits, part 2"

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index cf0910416c0d5e6aeb71c9b577b336f6eb21663a..719af78f7a40113544473225756f22213f1bfee9 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -6359,6 +6359,7 @@ class Integer : public Number {
                                    Heap::Space space = Heap::kNew);
 
   // Returns a canonical Integer object allocated in the old gen space.
+  // Returns null if integer is out of range (in --limit-ints-to-64-bits mode).
   static RawInteger* NewCanonical(const String& str);
 
   static RawInteger* New(int64_t value, Heap::Space space = Heap::kNew);
@@ -6604,6 +6605,9 @@ class Bigint : public Integer {
   // Returns a canonical Bigint object allocated in the old gen space.
   static RawBigint* NewCanonical(const String& str);
 
+  // Returns true if Bigint can't be instantiated.
+  static bool IsDisabled() { return FLAG_limit_ints_to_64_bits; }
+
  private:
   void SetNeg(bool value) const;
   void SetUsed(intptr_t value) const;