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

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index e4e89412d21958f3749269823278bfa3168e625c..7c2ea98baa228061322342643d4a4a8ec999a926 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -60,6 +60,7 @@ namespace internal {
   V(Oddball, true_value, TrueValue)                                            \
   V(Oddball, false_value, FalseValue)                                          \
   V(Oddball, uninitialized_value, UninitializedValue)                          \
+  V(Oddball, exception, Exception)                                             \
   V(Map, cell_map, CellMap)                                                    \
   V(Map, global_property_cell_map, GlobalPropertyCellMap)                      \
   V(Map, shared_function_info_map, SharedFunctionInfoMap)                      \
@@ -187,6 +188,7 @@ namespace internal {
   V(Map, uninitialized_map, UninitializedMap)                                  \
   V(Map, arguments_marker_map, ArgumentsMarkerMap)                             \
   V(Map, no_interceptor_result_sentinel_map, NoInterceptorResultSentinelMap)   \
+  V(Map, exception_map, ExceptionMap)                                          \
   V(Map, termination_exception_map, TerminationExceptionMap)                   \
   V(Map, message_object_map, JSMessageObjectMap)                               \
   V(Map, foreign_map, ForeignMap)                                              \