Move Kernel strings into the VM's heap.

runtime/vm/kernel_reader.h

Index: runtime/vm/kernel_reader.h
diff --git a/runtime/vm/kernel_reader.h b/runtime/vm/kernel_reader.h
index d9426fac2342255baf69a7dc4b3b9a193da5f440..8fda274d3d64d28ce1f09e6cb78a0b6c18b97053 100644
--- a/runtime/vm/kernel_reader.h
+++ b/runtime/vm/kernel_reader.h
@@ -66,6 +66,12 @@ class KernelReader {
 
   void ReadLibrary(Library* kernel_library);
 
+  const dart::String& DartSymbol(String* str) {
+    return translation_helper_.DartSymbol(str);
+  }
+
+  uint8_t CharacterAt(String* str, intptr_t index);
+
  private:
   friend class BuildingTranslationHelper;