Reapply "Move isolate loading to a separate loader isolate."

Source/bindings/dart/DartUtilities.h

Index: Source/bindings/dart/DartUtilities.h
diff --git a/Source/bindings/dart/DartUtilities.h b/Source/bindings/dart/DartUtilities.h
index 056c494a808495401e261563a0b7b0f85e2ad1a2..16171d31f66bf942ebd7fac2171c24287f5ee64d 100644
--- a/Source/bindings/dart/DartUtilities.h
+++ b/Source/bindings/dart/DartUtilities.h
@@ -171,6 +171,9 @@ public:
 
     static const uint8_t* fullSnapshot(Frame*);
 
+    static Dart_Handle canonicalizeUrl(Dart_Handle library, Dart_Handle urlHandle, String url);
+
+    static void reportProblem(ScriptExecutionContext*, const String&);
     static void reportProblem(ScriptExecutionContext*, Dart_Handle);
     static void reportProblem(ScriptExecutionContext*, Dart_Handle, const String& sourceURL);
 
@@ -194,6 +197,13 @@ public:
 
     static Dart_Handle invokeUtilsMethod(const char* methodName, int argCount, Dart_Handle* args);
 
+    static Dart_Handle convertSourceString(const String& source)
+    {
+        // FIXME: Decide whether to externalize this here.
+        const CString utf8encoded = source.utf8();
+        return Dart_NewStringFromCString(utf8encoded.data());
+    }
+
     static DartStringAdapter dartToString(Dart_Handle object, Dart_Handle& exception)
     {
         // FIXME: [performance] need better treatment of String vs. AtomicString, cf. v8 implementation.