Return MaybeHandle from NewRaw???String.

src/json-stringifier.h

Index: src/json-stringifier.h
diff --git a/src/json-stringifier.h b/src/json-stringifier.h
index 17c6b6f11141c52a589515f5d706371112411a8d..a083d48a09783348e2f006c212e0edda2ea6a8da 100644
--- a/src/json-stringifier.h
+++ b/src/json-stringifier.h
@@ -265,8 +265,7 @@ BasicJsonStringifier::BasicJsonStringifier(Isolate* isolate)
   accumulator_store_ = Handle<JSValue>::cast(
                            factory_->ToObject(factory_->empty_string()));
   part_length_ = kInitialPartLength;
-  current_part_ = factory_->NewRawOneByteString(part_length_);
-  ASSERT(!current_part_.is_null());
+  current_part_ = factory_->NewRawOneByteString(part_length_).ToHandleChecked();
   tojson_string_ = factory_->toJSON_string();
   stack_ = factory_->NewJSArray(8);
 }
@@ -308,18 +307,16 @@ MaybeObject* BasicJsonStringifier::StringifyString(Isolate* isolate,
   FlattenString(object);
   ASSERT(object->IsFlat());
   if (object->IsOneByteRepresentationUnderneath()) {
-    Handle<String> result =
-        isolate->factory()->NewRawOneByteString(worst_case_length);
-    ASSERT(!result.is_null());
+    Handle<String> result = isolate->factory()->NewRawOneByteString(
+        worst_case_length).ToHandleChecked();
     DisallowHeapAllocation no_gc;
     return StringifyString_<SeqOneByteString>(
         isolate,
         object->GetFlatContent().ToOneByteVector(),
         result);
   } else {
-    Handle<String> result =
-        isolate->factory()->NewRawTwoByteString(worst_case_length);
-    ASSERT(!result.is_null());
+    Handle<String> result = isolate->factory()->NewRawTwoByteString(
+        worst_case_length).ToHandleChecked();
     DisallowHeapAllocation no_gc;
     return StringifyString_<SeqTwoByteString>(
         isolate,
@@ -742,9 +739,11 @@ void BasicJsonStringifier::Extend() {
     part_length_ *= kPartLengthGrowthFactor;
   }
   if (is_ascii_) {
-    current_part_ = factory_->NewRawOneByteString(part_length_);
+    current_part_ =
+        factory_->NewRawOneByteString(part_length_).ToHandleChecked();
   } else {
-    current_part_ = factory_->NewRawTwoByteString(part_length_);
+    current_part_ =
+        factory_->NewRawTwoByteString(part_length_).ToHandleChecked();
   }
   ASSERT(!current_part_.is_null());
   current_index_ = 0;
@@ -754,7 +753,8 @@ void BasicJsonStringifier::Extend() {
 void BasicJsonStringifier::ChangeEncoding() {
   ShrinkCurrentPart();
   Accumulate();
-  current_part_ = factory_->NewRawTwoByteString(part_length_);
+  current_part_ =
+      factory_->NewRawTwoByteString(part_length_).ToHandleChecked();
   ASSERT(!current_part_.is_null());
   current_index_ = 0;
   is_ascii_ = false;