Move some Runtime:: functions and remove runtime.h as include when unnecessary.

src/runtime/string-builder.h

Index: src/runtime/string-builder.h
diff --git a/src/runtime/string-builder.h b/src/runtime/string-builder.h
index 37ff7b701858f96cc7fffb643ec24d6773f2d297..890b7f6be1bb0198c3681890991c29e142d42bf4 100644
--- a/src/runtime/string-builder.h
+++ b/src/runtime/string-builder.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef V8_STRING_BUILDER_H_
-#define V8_STRING_BUILDER_H_
+#ifndef V8_RUNTIME_STRING_BUILDER_H_
+#define V8_RUNTIME_STRING_BUILDER_H_
 
 namespace v8 {
 namespace internal {
@@ -293,4 +293,4 @@ class ReplacementStringBuilder {
 }
 }  // namespace v8::internal
 
-#endif  // V8_STRING_BUILDER_H_
+#endif  // V8_RUNTIME_STRING_BUILDER_H_