[runtime] Add PositiveNumberToUint32 helper to avoid double to uint roundtrip

src/conversions-inl.h

Index: src/conversions-inl.h
diff --git a/src/conversions-inl.h b/src/conversions-inl.h
index 2086f8184a1d212c8555d7d0fa4b24900be03fa7..d7789f9180880868baac232fbc4eeab9e58cb4d9 100644
--- a/src/conversions-inl.h
+++ b/src/conversions-inl.h
@@ -128,12 +128,26 @@ int32_t NumberToInt32(Object* number) {
   return DoubleToInt32(number->Number());
 }
 
-
 uint32_t NumberToUint32(Object* number) {
   if (number->IsSmi()) return Smi::cast(number)->value();
   return DoubleToUint32(number->Number());
 }
 
+uint32_t PositiveNumberToUint32(Object* number) {
+  if (number->IsSmi()) {
+    int value = Smi::cast(number)->value();
+    if (value <= 0) return 0;
+    return value;
+  }
+  DCHECK(number->IsHeapNumber());
+  double value = number->Number();
+  // Catch all values smaller than 1 and use the double-negation trick for NANs.
+  if (!(value >= 1)) return 0;
+  uint32_t max = std::numeric_limits<uint32_t>::max();
+  if (value < max) return static_cast<uint32_t>(value);
+  return max;
+}
+
 int64_t NumberToInt64(Object* number) {
   if (number->IsSmi()) return Smi::cast(number)->value();
   return static_cast<int64_t>(number->Number());