[WIP] Move layout states into the DocumentLifecycle state machine

Source/core/dom/DocumentLifecycle.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  */
 
 #include "config.h"
 #include "core/dom/DocumentLifecycle.h"
 
 #include "wtf/Assertions.h"
 #include <stdio.h>
 
 namespace WebCore {
 
+static DocumentLifecycle::DeprecatedTransition* s_deprecatedTransitionStack = 0;
+
+DocumentLifecycle::Scope::Scope(DocumentLifecycle& lifecycle, State finalState)
+    : m_lifecycle(lifecycle)
+    , m_finalState(finalState)
+{
+}
+
+DocumentLifecycle::Scope::~Scope()
+{
+    m_lifecycle.advanceTo(m_finalState);
+}
+
+DocumentLifecycle::DeprecatedTransition::DeprecatedTransition(State from, State to)
+    : m_previous(s_deprecatedTransitionStack)
+    , m_from(from)
+    , m_to(to)
+{
+    s_deprecatedTransitionStack = this;
+}
+
+DocumentLifecycle::DeprecatedTransition::~DeprecatedTransition()
+{
+    s_deprecatedTransitionStack = m_previous;
+}
+
 DocumentLifecycle::DocumentLifecycle()
     : m_state(Uninitialized)
 {
 }
 
 DocumentLifecycle::~DocumentLifecycle()
 {
 }
 
+#if !ASSERT_DISABLED
+
+static bool isClean(DocumentLifecycle::State state)
+{
+    return state == DocumentLifecycle::StyleClean || state == DocumentLifecycle::LayoutClean;
+}
+
 bool DocumentLifecycle::canAdvanceTo(State state) const
 {
+    // This transition is bogus, but we've whitelisted it anyway.
+    if (s_deprecatedTransitionStack && m_state == s_deprecatedTransitionStack->from() && state == s_deprecatedTransitionStack->to())
+        return true;
+
     if (state > m_state)
         return true;
     // FIXME: We can dispose a document multiple times. This seems wrong.
     // See https://code.google.com/p/chromium/issues/detail?id=301668.
-    if (m_state == Disposed)
+    if (m_state == Disposed) {
         return state == Disposed;
-    if (m_state == Clean) {
-        // We can synchronously enter recalc style without rewinding to
-        // StyleRecalcPending.
-        return state == InStyleRecalc;
+    } else if (isClean(m_state)) {
+        if (state == StyleRecalcPending)
+            return true;
+        // We can synchronously recalc style.
+        if (state == InStyleRecalc)

[ojan, 2014/02/06 05:11:39]

Do we really go from LayoutClean to InStyleRecalc without a pitstop in
StyleRecalcPending? 

[abarth-chromium, 2014/02/06 05:31:15]

I'm not sure.  We can split out those two states to see what transitions they
have.

[ojan, 2014/02/06 20:36:10]

Yeah, that was what I had in mind. It's was a bit surprising to me to group
these two states together.

+            return true;
+        // We can synchronously perform layout.
+        if (state == InPreLayout)
+            return true;
+        if (state == InPerformLayout)
+            return true;
+        if (isClean(state))
+            return true;
+        return false;
+    } else if (m_state == InPreLayout) {
+        return state == InStyleRecalc || state == StyleClean;
+    } else if (m_state == AfterPerformLayout) {
+        return state == InPreLayout;

[ojan, 2014/02/06 05:11:39]

This is for partialLayout?

[abarth-chromium, 2014/02/06 05:31:15]

This case comes up for scroll bars.  After layout, we resize the scrollbars,
which causes us to need to layout again.  When we unwind the stack, everything
is clean.

     }
     return false;
 }
 
+#endif
+
 void DocumentLifecycle::advanceTo(State state)
 {
     ASSERT(canAdvanceTo(state));
     m_state = state;
 }
 
 void DocumentLifecycle::rewindTo(State state)
 {
-    ASSERT(m_state == Clean);
-    ASSERT(state < m_state);
-    m_state = state;
-    ASSERT(isActive());
+    advanceTo(state);
 }
 
 }