Port sky-scrollable to Dart

sky/engine/core/html/parser/HTMLDocumentParser.cpp

Index: sky/engine/core/html/parser/HTMLDocumentParser.cpp
diff --git a/sky/engine/core/html/parser/HTMLDocumentParser.cpp b/sky/engine/core/html/parser/HTMLDocumentParser.cpp
index 08087fcb885f615a81b516e92bc77d7ddff12cd4..9f2ab19ed6df9f3be5059df04814b4090759b45d 100644
--- a/sky/engine/core/html/parser/HTMLDocumentParser.cpp
+++ b/sky/engine/core/html/parser/HTMLDocumentParser.cpp
@@ -394,11 +394,12 @@ bool HTMLDocumentParser::isWaitingForScripts() const
 
 void HTMLDocumentParser::resumeAfterWaitingForImports()
 {
-    RefPtr<HTMLDocumentParser> protect(this);
-    ASSERT(!isWaitingForScripts());

[abarth-chromium, 2015/02/21 09:15:49]

sky/examples/example-scrollable/index.sky hits this ASSERT.  I need to make a
reduced test case for sky/tests.

+    if (isWaitingForScripts())
+        return;
     if (m_pendingChunks.isEmpty())
         return;
     ASSERT(m_haveBackgroundParser);
+    RefPtr<HTMLDocumentParser> protect(this);
     pumpPendingChunks();
 }