Reduce header files including header files.

Main focus is getting heap.h out of runtime.h.

Change-Id: I8d13dce8512816db2820a27b24f5866cc871a04b
diff --git a/runtime/utils.cc b/runtime/utils.cc
index f562252..dd64e52 100644
--- a/runtime/utils.cc
+++ b/runtime/utils.cc
@@ -552,6 +552,18 @@
   }
 }
 
+std::string PrintableChar(uint16_t ch) {
+  std::string result;
+  result += '\'';
+  if (NeedsEscaping(ch)) {
+    StringAppendF(&result, "\\u%04x", ch);
+  } else {
+    result += ch;
+  }
+  result += '\'';
+  return result;
+}
+
 std::string PrintableString(const std::string& utf) {
   std::string result;
   result += '"';