Avoid calling a virtual method on a null document in lifecycle().

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 1e1bf54b71d6690470c8e3bd803e423ea33ab088..c380e310f2542f72e4dc790659887ac73905d7fb 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -1366,6 +1366,8 @@ FloatSize FrameView::viewportSizeForViewportUnits() const {
 }
 
 DocumentLifecycle& FrameView::lifecycle() const {
+  DCHECK(m_frame);
+  DCHECK(m_frame->document());
   return m_frame->document()->lifecycle();
 }
 
@@ -4599,7 +4601,8 @@ void FrameView::maybeRecordLoadReason() {
 }
 
 bool FrameView::shouldThrottleRendering() const {
-  return canThrottleRendering() && lifecycle().throttlingAllowed();
+  return canThrottleRendering() && m_frame->document() &&
+         lifecycle().throttlingAllowed();
 }
 
 bool FrameView::canThrottleRendering() const {