[bigint] Adapt Object::BooleanValue().

R=jkummerow@chromium.org

Bug: v8:6791
Change-Id: Id050eb583af2977e27a91f6ff9ab82c72df0ca2e
Reviewed-on: https://chromium-review.googlesource.com/711849Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48488}

src/objects.cc

@@ -469,6 +469,7 @@ bool Object::BooleanValue() {
   if (IsUndetectable()) return false;  // Undetectable object is false.
   if (IsString()) return String::cast(this)->length() != 0;
   if (IsHeapNumber()) return DoubleToBoolean(HeapNumber::cast(this)->value());
+  if (IsBigInt()) return BigInt::cast(this)->ToBoolean();
   return true;
 }
 

test/mjsunit/harmony/bigint.js

@@ -241,6 +241,10 @@ const six = BigInt(6);
   assertFalse(!one);
   assertTrue(!!one);
   assertFalse(!!!one);
+
+  // This is a hack to test Object::BooleanValue.
+  assertTrue(%CreateIterResultObject(42, one).done);
+  assertFalse(%CreateIterResultObject(42, zero).done);
 }
 
 // Strict equality