[vm] Change TypedData_getUint64 native method to silently cast values

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index c5faed86ee98228f863825674ed14900e357236c..269decc2b7ccaab4b3e1bbfd43c76f344c4b76c3 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -18155,15 +18155,18 @@ RawInteger* Integer::New(int64_t value, Heap::Space space) {
 }
 
 RawInteger* Integer::NewFromUint64(uint64_t value, Heap::Space space) {
-  if (value > static_cast<uint64_t>(Mint::kMaxValue)) {
-    if (FLAG_limit_ints_to_64_bits) {
-      // Out of range.
-      return Integer::null();
-    } else {
-      return Bigint::NewFromUint64(value, space);
-    }
+  if (!FLAG_limit_ints_to_64_bits &&
+      (value > static_cast<uint64_t>(Mint::kMaxValue))) {
+    return Bigint::NewFromUint64(value, space);
+  }
+  return Integer::New(static_cast<int64_t>(value), space);
+}
+
+bool Integer::IsValidUint64(uint64_t value) {
+  if (FLAG_limit_ints_to_64_bits) {
+    return (value <= static_cast<uint64_t>(Mint::kMaxValue));
   } else {
-    return Integer::New(value, space);

[siva, 2017/07/31 21:46:08]

why is it not ok to just change this to 
  return Integer::New(static_cast<int64_t>(value), space);

and not have this new function IsValidUint64 ... and drop the changes in
Dart_NewIntegerFromUint64

[alexmarkov, 2017/07/31 23:58:12]

Integer::NewFromUint64 is called from 2 places: Dart_NewIntegerFromUint64 and
TypedData_getUint64. The latter requires silent wrap-around, so range checking
is moved to Dart_NewIntegerFromUint64.

As per our discussion, I'm going to rename Integer::IsValidUint64 in order to
improve readability in the follow-up CL:
https://codereview.chromium.org/2992783002/

+    return true;
   }
 }