[bigint] Adapt Object::StrictEquals.

R=jkummerow@chromium.org

Bug: v8:6791
Change-Id: I7e99a8aa2aa65e78a8d4288f496d496600063bfe
Reviewed-on: https://chromium-review.googlesource.com/712534
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48485}

src/objects.cc

@@ -623,6 +623,9 @@ bool Object::StrictEquals(Object* that) {
   } else if (this->IsString()) {
     if (!that->IsString()) return false;
     return String::cast(this)->Equals(String::cast(that));
+  } else if (this->IsBigInt()) {
+    if (!that->IsBigInt()) return false;
+    return BigInt::Equal(BigInt::cast(this), BigInt::cast(that));
   }
   return this == that;
 }

test/mjsunit/harmony/bigint.js

@@ -260,6 +260,22 @@ const six = BigInt(6);
   assertTrue(zero !== 0);
   assertFalse(0 === zero);
   assertTrue(0 !== zero);
+}{
+  assertTrue(%StrictEqual(zero, zero));
+  assertFalse(%StrictNotEqual(zero, zero));
+
+  assertTrue(%StrictEqual(zero, another_zero));
+  assertFalse(%StrictNotEqual(zero, another_zero));
+
+  assertFalse(%StrictEqual(zero, one));
+  assertTrue(%StrictNotEqual(zero, one));
+  assertTrue(%StrictNotEqual(one, zero));
+  assertFalse(%StrictEqual(one, zero));
+
+  assertFalse(%StrictEqual(zero, 0));
+  assertTrue(%StrictNotEqual(zero, 0));
+  assertFalse(%StrictEqual(0, zero));
+  assertTrue(%StrictNotEqual(0, zero));
 }
 
 // SameValue