Model each Dart library as its own ScriptState when devtools are enabled.

Source/bindings/dart/DartHandleProxy.h

Index: Source/bindings/dart/DartHandleProxy.h
diff --git a/Source/bindings/dart/DartHandleProxy.h b/Source/bindings/dart/DartHandleProxy.h
index 96c77dfaa22df6ee35c3f75c39dfb8e0ab232bb6..6d4132c19d947165168721ebe1ffbd10ae0d78ee 100644
--- a/Source/bindings/dart/DartHandleProxy.h
+++ b/Source/bindings/dart/DartHandleProxy.h
@@ -49,6 +49,7 @@ public:
     static v8::Handle<v8::Value> createTypeProxy(Dart_Handle value, bool showStatics);
     static v8::Handle<v8::Value> createLibraryProxy(Dart_Handle value, int32_t libraryId, Dart_Handle prefix);
     static v8::Handle<v8::Value> createLocalScopeProxy(Dart_Handle localVariables);
+    static v8::Handle<v8::Value> evaluate(Dart_Handle target, Dart_Handle expression, Dart_Handle localVariables);
 
     static bool isDartProxy(v8::Handle<v8::Value>);
     static const char* getJavaScriptType(v8::Handle<v8::Value>);
@@ -67,11 +68,12 @@ private:
     DartIsolateScope scope;
     DartApiScope apiScope;
     Dart_ExceptionPauseInfo previousPauseInfo;
+    bool disableBreak;
 
 public:
     Dart_PersistentHandle handle;
 
-    DartScopes(v8::Local<v8::Object> v8Handle);
+    DartScopes(v8::Local<v8::Object> v8Handle, bool disableBreak = false);
     ~DartScopes();
 };