Add infrastructure for partial layouts

Source/core/page/FrameView.cpp

Index: Source/core/page/FrameView.cpp
diff --git a/Source/core/page/FrameView.cpp b/Source/core/page/FrameView.cpp
index 7f2dee31eb9a88cfc60fc1249c137760f2dda08f..74f0a48b1634add63c589a22b6ea45a96e8f23ae 100644
--- a/Source/core/page/FrameView.cpp
+++ b/Source/core/page/FrameView.cpp
@@ -179,6 +179,8 @@ FrameView::FrameView(Frame* frame)
     , m_didRunAutosize(false)
     , m_hasSoftwareFilters(false)
     , m_visibleContentScaleFactor(1)
+    , m_shouldStopPartialLayout(false)
+    , m_stopLayoutAtRenderer(0)
 {
     init();
 
@@ -848,6 +850,8 @@ void FrameView::layout(bool allowSubtree)
     if (m_inLayout)
         return;
 
+    ASSERT(!shouldStopPartialLayout());
+
     TRACE_EVENT0("webkit", "FrameView::layout");
     TRACE_EVENT_SCOPED_SAMPLING_STATE("Blink", "Layout");
 
@@ -985,6 +989,15 @@ void FrameView::layout(bool allowSubtree)
 
         m_actionScheduler->pause();
 
+        // Text Autosizing requires two-pass layout which is incompatible with partial layout. If
+        // enabled, only do partial layout for the second layout.
+        // FIXME (crbug.com/256657): Do not do two layouts for text autosizing.
+        RenderObject* delayPartialLayoutForRenderer = 0;
+        if (m_frame->settings() && m_frame->settings()->textAutosizingEnabled()) {

[eseidel, 2013/08/20 21:00:39]

You don't need all this if you add a "m_disablePartialLayoutCount" and just
increment it for the first layout when textAutosigingEnabled is true.

// We need to disable partial layouts for the first layout if we might
// end up doing two-pass layout for autosizing.
PartialLayoutDisabler disabler(m_frame->settings()->textAutosizingEnabled());

[pdr., 2013/08/26 05:50:40]

Done.

+            delayPartialLayoutForRenderer = m_stopLayoutAtRenderer;
+            m_stopLayoutAtRenderer = 0;
+        }
+
         {
             bool disableLayoutState = false;
             if (inSubtreeLayout) {
@@ -999,6 +1012,11 @@ void FrameView::layout(bool allowSubtree)
             forceLayoutParentViewIfNeeded();
             rootForThisLayout->layout();
 
+            // If text autosizing is enabled, do a partial layout for the second layout.
+            if (delayPartialLayoutForRenderer) {
+                ASSERT(!shouldStopPartialLayout());
+                m_stopLayoutAtRenderer = delayPartialLayoutForRenderer;
+            }
             bool autosized = document->textAutosizer()->processSubtree(rootForThisLayout);
             if (autosized && rootForThisLayout->needsLayout()) {
                 TRACE_EVENT0("webkit", "2nd layout due to Text Autosizing");
@@ -1014,6 +1032,13 @@ void FrameView::layout(bool allowSubtree)
         m_layoutRoot = 0;
     } // Reset m_layoutSchedulingEnabled to its previous value.
 
+    // Reset partial layout state post-layout and exit here if a partial layout was done.
+    if (shouldStopPartialLayout()) {
+        resetPartialLayoutState();
+        return;
+    }
+    resetPartialLayoutState();

[eseidel, 2013/08/20 21:00:39]

Shouldn't the original caller drive this?

[pdr., 2013/08/26 05:50:40]

Fixing this was enlightening. resetPartialLayoutState() was masking a bug.

We disable overlay scrollbars when running tests (for cross-platform
consistency). Because non-overlay scrollbars cause a second layout through
adjustViewSize(), I've added a PartialLayoutDisabler for the primary layout. In
the common case, the first ("primary?") layout will early-out if scrollbars are
present, so we should still have a nice speed win.

I've also changed this so the original caller
(partialUpdateLayoutIgnorePendingStylesheets) is now the one to call reset().

I've added two tests to prove this works.

+
     bool neededFullRepaint = m_doFullRepaint;
 
     if (!inSubtreeLayout && !toRenderView(rootForThisLayout)->printing())
@@ -1097,6 +1122,17 @@ void FrameView::layout(bool allowSubtree)
         frame()->page()->chrome().client()->layoutUpdated(frame());
 }
 
+#ifndef NDEBUG
+void FrameView::checkPartialLayoutAllowed()
+{
+    RenderObject* renderer = m_stopLayoutAtRenderer;
+    while (renderer) {

[esprehn, 2013/08/23 20:47:27]

This could be a for() loop :)

[pdr., 2013/08/26 05:50:40]

This function was useful for checking my logic in writing this patch, but it's
no longer all that useful (it's redundant since we do this check in
Document::partialUpdateLayoutIgnorePendingStylesheets). I've removed this for
now.

+        ASSERT(renderer->supportsPartialLayout());
+        renderer = renderer->parent();
+    }
+}
+#endif
+
 RenderBox* FrameView::embeddedContentBox() const
 {
     RenderView* renderView = this->renderView();