[vm] Change TypedData_getUint64 native method to silently cast values

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index ed2c2c13ce9c63bf2b246838ef52332f122e69b2..105de78e6e086fe44e4a960c186c3c9238e800f7 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -6422,6 +6422,10 @@ class Number : public Instance {
 class Integer : public Number {
  public:
   static RawInteger* New(const String& str, Heap::Space space = Heap::kNew);
+
+  // Creates a new Integer by given uint64_t value.
+  // In the --limit-ints-to-64-bits mode silently casts value to int64_t
+  // (with wrap-around if it is greater than kMaxInt64).
   static RawInteger* NewFromUint64(uint64_t value,
                                    Heap::Space space = Heap::kNew);
 
@@ -6431,6 +6435,9 @@ class Integer : public Number {
 
   static RawInteger* New(int64_t value, Heap::Space space = Heap::kNew);
 
+  // Returns true iff the given uint64_t value is representable as Dart integer.
+  static bool IsValidUint64(uint64_t value);
+
   virtual bool OperatorEquals(const Instance& other) const {
     return Equals(other);
   }