d8 external array c'tors: fix double-to-uint32 semantics

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 9390c846d60055aef88431c04c70761dcfb00aac..544e824870d03a51a9229b05f754430f991f1c5a 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -300,11 +300,11 @@ Handle<Value> Shell::CreateExternalArray(const Arguments& args,
     if (number.IsEmpty() || !number->IsNumber()) {
       return ThrowException(String::New("Array length must be a number."));
     }
-    double raw_length = number->NumberValue();
+    int32_t raw_length = number->ToInt32()->Int32Value();
     if (raw_length < 0) {
       return ThrowException(String::New("Array length must not be negative."));
     }
-    if (raw_length > kMaxLength) {
+    if (raw_length > static_cast<int32_t>(kMaxLength)) {
       return ThrowException(
           String::New("Array length exceeds maximum length."));
     }