Add string encoding to wire protocol

runtime/include/dart_debugger_api.h

Index: runtime/include/dart_debugger_api.h
===================================================================
--- runtime/include/dart_debugger_api.h	(revision 8218)
+++ runtime/include/dart_debugger_api.h	(working copy)
@@ -82,6 +82,8 @@
 
 
 /**
+ * DEPRECATED --- use Dart_ScriptGetSource
+ *
  * Returns a string containing the source code of the given script
  * in the given library.
  *
@@ -96,6 +98,20 @@
 
 
 /**
+ * Returns a string containing the source code of the given script
+ * in the given library.
+ *
+ * Requires there to be a current isolate.
+ *
+ * \return A handle to string containing the source text if no error
+ * occurs.
+ */
+DART_EXPORT Dart_Handle Dart_ScriptGetSource(
+                            intptr_t library_id,
+                            Dart_Handle script_url_in);
+
+
+/**
  * Sets a breakpoint at line \line_number in \script_url, or the closest
  * following line (within the same function) where a breakpoint can be set.
  *