Don't bother layout until first navigation is done.

third_party/WebKit/Source/core/layout/LayoutTestHelper.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/LayoutTestHelper.h"
 
 #include "core/frame/FrameHost.h"
 #include "core/html/HTMLIFrameElement.h"
+#include "core/loader/FrameLoaderStateMachine.h"
 #include "platform/graphics/test/FakeGraphicsLayerFactory.h"
 #include "platform/scroll/ScrollbarTheme.h"
 
 namespace blink {
 
 namespace {
 
 class FakeChromeClient : public EmptyChromeClient {
 public:
     static PassOwnPtrWillBeRawPtr<FakeChromeClient> create() { return adoptPtrWillBeNoop(new FakeChromeClient); }
@@ skipping 35 matching lines @@
     }
 
     // We need to destroy most of the Blink structure here because derived tests may restore
     // RuntimeEnabledFeatures setting during teardown, which happens before our destructor
     // getting invoked, breaking the assumption that REF can't change during Blink lifetime.
     m_pageHolder = nullptr;
 }
 
 Document& RenderingTest::setupChildIframe(const AtomicString& iframeElementId, const String& htmlContentOfIframe)
 {
-
     HTMLIFrameElement& iframe = *toHTMLIFrameElement(document().getElementById(iframeElementId));
     m_childFrameLoaderClient = FrameLoaderClientWithParent::create(document().frame());
     m_subframe = LocalFrame::create(m_childFrameLoaderClient.get(), document().frame()->host(), &iframe);
     m_subframe->setView(FrameView::create(m_subframe.get(), IntSize(500, 500)));
     m_subframe->init();
+    // Some tests directly inject content into the initial empty document.
+    // Unmark it so that unforced layout would also run on the document.
+    m_subframe->loader().stateMachine()->advanceTo(FrameLoaderStateMachine::CommittedFirstRealLoad);
     m_subframe->view()->setParentVisible(true);
     m_subframe->view()->setSelfVisible(true);
     static_cast<SingleChildFrameLoaderClient*>(document().frame()->client())->setChild(m_subframe.get());
     document().frame()->host()->incrementSubframeCount();
     Document& frameDocument = *iframe.contentDocument();
 
     frameDocument.setBaseURLOverride(KURL(ParsedURLString, "http://test.com"));
     frameDocument.body()->setInnerHTML(htmlContentOfIframe, ASSERT_NO_EXCEPTION);
     return frameDocument;
 }
 
 } // namespace blink