Make LiteralBuffer + LiteralScope private.

Reduce the Scanner API, in order to make subsequent rework easier.

R=marja@chromium.org
BUG=v8:4947

Review-Url: https://codereview.chromium.org/2192883002
Cr-Commit-Position: refs/heads/master@{#38522}

src/parsing/parser.cc

@@ -5365,13 +5365,12 @@ IterationStatement* Parser::LookupContinueTarget(const AstRawString* label,
 
 
 void Parser::HandleSourceURLComments(Isolate* isolate, Handle<Script> script) {
-  if (scanner_.source_url()->length() > 0) {
-    Handle<String> source_url = scanner_.source_url()->Internalize(isolate);
+  Handle<String> source_url = scanner_.SourceUrl(isolate);
+  if (!source_url.is_null()) {
     script->set_source_url(*source_url);
   }
-  if (scanner_.source_mapping_url()->length() > 0) {
-    Handle<String> source_mapping_url =
-        scanner_.source_mapping_url()->Internalize(isolate);
+  Handle<String> source_mapping_url = scanner_.SourceMappingUrl(isolate);
+  if (!source_mapping_url.is_null()) {
     script->set_source_mapping_url(*source_mapping_url);
   }
 }

src/parsing/scanner.cc

@@ -19,8 +19,7 @@
 namespace v8 {
 namespace internal {
 
-
-Handle<String> LiteralBuffer::Internalize(Isolate* isolate) const {
+Handle<String> Scanner::LiteralBuffer::Internalize(Isolate* isolate) const {
   if (is_one_byte()) {
     return isolate->factory()->InternalizeOneByteString(one_byte_literal());
   }