Don't bother layout until first navigation is done.

third_party/WebKit/Source/core/testing/DummyPageHolder.cpp

Index: third_party/WebKit/Source/core/testing/DummyPageHolder.cpp
diff --git a/third_party/WebKit/Source/core/testing/DummyPageHolder.cpp b/third_party/WebKit/Source/core/testing/DummyPageHolder.cpp
index 2e9b253d93c91c7faa096fc4c3a1c8d7e6a5d08c..41e72c69703149fe4d9dd96b19b50da1acf39476 100644
--- a/third_party/WebKit/Source/core/testing/DummyPageHolder.cpp
+++ b/third_party/WebKit/Source/core/testing/DummyPageHolder.cpp
@@ -36,6 +36,7 @@
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/loader/EmptyClients.h"
+#include "core/loader/FrameLoaderStateMachine.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
@@ -85,6 +86,9 @@ DummyPageHolder::DummyPageHolder(
     m_frame->setView(FrameView::create(m_frame.get(), initialViewSize));
     m_frame->view()->page()->frameHost().visualViewport().setSize(initialViewSize);
     m_frame->init();
+    // Some tests directly inject content into the initial empty document.
+    // Unmark it so that unforced layout would also run on the document.
+    m_frame->loader().stateMachine()->advanceTo(FrameLoaderStateMachine::CommittedFirstRealLoad);
 }
 
 DummyPageHolder::~DummyPageHolder()