[compiler] Introduce code stubs for abstract equality.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 4a44e661de59c04c63cc1e5bb498c51ca6bc88f8..b9e48ba96c0fe12574f3293047550b22b5f6448c 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -285,6 +285,10 @@ Maybe<ComparisonResult> Object::Compare(Handle<Object> x, Handle<Object> y) {
 
 // static
 Maybe<bool> Object::Equals(Handle<Object> x, Handle<Object> y) {
+  // This is the generic version of Abstract Equality Comparison; a version in
+  // JavaScript land is available in the EqualStub and NotEqualStub. Whenever
+  // you change something functionality wise in here, remember to update the
+  // TurboFan code stubs as well.
   while (true) {
     if (x->IsNumber()) {
       if (y->IsNumber()) {