Introduce exception object and remove some uses of MaybeObject::IsFailure().

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index aa826141244413cdff2b3d0a362a5ed9153e5e19..1b6fabf7b63199fd91090241e43f7f55839beba1 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -612,7 +612,7 @@ void Oddball::OddballVerify() {
     CHECK(number->IsSmi());
     int value = Smi::cast(number)->value();
     // Hidden oddballs have negative smis.
-    const int kLeastHiddenOddballNumber = -4;
+    const int kLeastHiddenOddballNumber = -5;
     CHECK_LE(value, 1);
     CHECK(value >= kLeastHiddenOddballNumber);
   }
@@ -633,6 +633,8 @@ void Oddball::OddballVerify() {
     CHECK(this == heap->arguments_marker());
   } else if (map() == heap->termination_exception_map()) {
     CHECK(this == heap->termination_exception());
+  } else if (map() == heap->exception_map()) {
+    CHECK(this == heap->exception());
   } else {
     UNREACHABLE();
   }