Advance document lifecycle to CompositingClean prior to hit testing

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 112 matching lines @@
         // can happen when we call layout recursively and we unwind the stack.
         if (state == LayoutClean)
             return true;
         if (state == StyleClean)
             return true;
         return false;
     }
     if (m_state == CompositingClean) {
         if (state == InStyleRecalc)
             return true;
+        if (state == InPreLayout)

[esprehn, 2015/03/24 23:01:03]

If we're in pre layout tasks why would we advance directly to CompositingClean?
This patch doesn't seem to explain the reason for this.

[qiankun, 2015/03/25 03:13:59]

It allows advancing document life cycle from CompositingClean to preLayout. I
fixed the case calls layout() after hit testing.

There is no bug for hit testing. This change is motivated by
https://codereview.chromium.org/976543002. In order to query compositingState in
collectFragments(), levi@ and chrishtr@ suggested that we should ensure that the
document lifecycle is advanced to CompositingClean prior to hit testing.

+            return true;
         if (state == InCompositingUpdate)
             return true;
         if (state == InPaintInvalidation)
             return true;
         return false;
     }
     if (m_state == InPaintInvalidation) {
         if (state == PaintInvalidationClean)
             return true;
         return false;
@@ skipping 29 matching lines @@
 void DocumentLifecycle::ensureStateAtMost(State state)
 {
     ASSERT(state == VisualUpdatePending || state == StyleClean || state == LayoutClean);
     if (m_state <= state)
         return;
     ASSERT(canRewindTo(state));
     m_state = state;
 }
 
 }