[iwyu] Include handles.h less.

src/parsing/scanner-character-streams.h

Index: src/parsing/scanner-character-streams.h
diff --git a/src/parsing/scanner-character-streams.h b/src/parsing/scanner-character-streams.h
index b9c28248dc209d1366a313c6ef6f6cfab809b6b7..291765cee49f6b8adf4c297a74151e3d0fcefeb7 100644
--- a/src/parsing/scanner-character-streams.h
+++ b/src/parsing/scanner-character-streams.h
@@ -6,13 +6,15 @@
 #define V8_PARSING_SCANNER_CHARACTER_STREAMS_H_
 
 #include "include/v8.h"  // for v8::ScriptCompiler
-#include "src/handles.h"
 
 namespace v8 {
 namespace internal {
 
+template <typename T>
+class Handle;
 class Utf16CharacterStream;
 class RuntimeCallStats;
+class String;
 
 class ScannerStream {
  public: