Using GetMoreGeneralElementsKind in more places

BUG=

Review URL: https://codereview.chromium.org/1338983003

Cr-Commit-Position: refs/heads/master@{#30715}

src/builtins.cc

@@ -1228,19 +1228,15 @@ Object* Slow_ArrayConcat(Arguments* args, Isolate* isolate) {
       if (length_estimate != 0) {
         ElementsKind array_kind =
             GetPackedElementsKind(array->map()->elements_kind());
-        if (IsMoreGeneralElementsKindTransition(kind, array_kind)) {
-          kind = array_kind;
-        }
+        kind = GetMoreGeneralElementsKind(kind, array_kind);
       }
       element_estimate = EstimateElementCount(array);
     } else {
       if (obj->IsHeapObject()) {
         if (obj->IsNumber()) {
-          if (IsMoreGeneralElementsKindTransition(kind, FAST_DOUBLE_ELEMENTS)) {
-            kind = FAST_DOUBLE_ELEMENTS;
-          }
-        } else if (IsMoreGeneralElementsKindTransition(kind, FAST_ELEMENTS)) {
-          kind = FAST_ELEMENTS;
+          kind = GetMoreGeneralElementsKind(kind, FAST_DOUBLE_ELEMENTS);
+        } else {
+          kind = GetMoreGeneralElementsKind(kind, FAST_ELEMENTS);
         }
       }
       length_estimate = 1;

src/elements.cc

@@ -2375,9 +2375,7 @@ Handle<JSArray> ElementsAccessor::Concat(Isolate* isolate, Arguments* args,
       ElementsKind arg_kind = JSArray::cast(arg)->map()->elements_kind();
       has_double = has_double || IsFastDoubleElementsKind(arg_kind);
       is_holey = is_holey || IsFastHoleyElementsKind(arg_kind);
-      if (IsMoreGeneralElementsKindTransition(elements_kind, arg_kind)) {
-        elements_kind = arg_kind;
-      }
+      elements_kind = GetMoreGeneralElementsKind(elements_kind, arg_kind);
     }
     if (is_holey) {
       elements_kind = GetHoleyElementsKind(elements_kind);