<< operator for CodeWriter

Adding << operator to CodeWriter.

Test: m -j
Test: runtests.sh

Change-Id: Ieec617496251705c060f8f62d8b001dae325aa2b
diff --git a/code_writer.h b/code_writer.h
index 2a81dac..aea50ef 100644
--- a/code_writer.h
+++ b/code_writer.h
@@ -48,6 +48,9 @@
   virtual ~CodeWriter() = default;
   CodeWriter() = default;
 
+  CodeWriter& operator<<(const char* s);
+  CodeWriter& operator<<(const std::string& str);
+
  private:
   CodeWriter(std::unique_ptr<std::ostream> ostream);
   std::string ApplyIndent(const std::string& str);