Teach SkyView code path to print hello, world

sky/engine/core/script/dom_dart_state.cc

Index: sky/engine/core/script/dom_dart_state.cc
diff --git a/sky/engine/core/script/dom_dart_state.cc b/sky/engine/core/script/dom_dart_state.cc
index dfc7a5c84bbe5c597e06309c00142e209f79a1e6..8f5784b58259a3bb6bd310deffb4bd253daf3a8e 100644
--- a/sky/engine/core/script/dom_dart_state.cc
+++ b/sky/engine/core/script/dom_dart_state.cc
@@ -12,7 +12,6 @@ namespace blink {
 
 DOMDartState::DOMDartState(Document* document)
     : document_(document), loader_(adoptPtr(new DartLoader(this))) {
-  DCHECK(document_);
 }
 
 DOMDartState::~DOMDartState() {
@@ -27,10 +26,12 @@ Document* DOMDartState::CurrentDocument() {
 }
 
 LocalFrame* DOMDartState::CurrentFrame() {
+  DCHECK(Current()->document_);
   return Current()->document_->frame();
 }
 
 LocalDOMWindow* DOMDartState::CurrentWindow() {
+  DCHECK(Current()->document_);
   return Current()->document_->domWindow();
 }