[FrameView::layout cleanup] Move post layout task scheduling logic to…

… a separate function

https://bugs.webkit.org/show_bug.cgi?id=178538
<rdar://problem/35080743>

Reviewed by Simon Fraser.

Move and reorganize post layout task scheduling code.

Covered by existing tests.

* page/FrameView.cpp:
(WebCore::FrameView::layout):
(WebCore::FrameView::runOrSchedulePostLayoutTasks):
* page/FrameView.h:


Canonical link: https://commits.webkit.org/194732@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@223717 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,20 @@
+2017-10-19  Zalan Bujtas  <zalan@apple.com>
+
+        [FrameView::layout cleanup] Move post layout task scheduling logic to a separate function
+        https://bugs.webkit.org/show_bug.cgi?id=178538
+        <rdar://problem/35080743>
+
+        Reviewed by Simon Fraser.
+
+        Move and reorganize post layout task scheduling code.
+
+        Covered by existing tests.
+
+        * page/FrameView.cpp:
+        (WebCore::FrameView::layout):
+        (WebCore::FrameView::runOrSchedulePostLayoutTasks):
+        * page/FrameView.h:
+
 2017-10-19  Zalan Bujtas  <zalan@apple.com>
 
         [FrameView::layout cleanup] Move scrollbars setup logic to a separate function

Source/WebCore/page/FrameView.cpp

@@ -1548,28 +1548,40 @@ void FrameView::layout(bool allowSubtreeLayout)
 
     frame().document()->markers().invalidateRectsForAllMarkers();
 
-    if (!m_postLayoutTasksTimer.isActive()) {
-        if (!m_inPerformPostLayoutTasks) {
-            if (isInChildFrameWithFrameFlattening())
-                updateWidgetPositions();
-            else
-                performPostLayoutTasks(); // Calls resumeScheduledEvents().
-        }
-
-        if (!m_postLayoutTasksTimer.isActive() && (needsLayout() || m_inPerformPostLayoutTasks || isInChildFrameWithFrameFlattening())) {
-            // If we need layout or are already in a synchronous call to postLayoutTasks(), 
-            // defer widget updates and event dispatch until after we return. postLayoutTasks()
-            // can make us need to update again, and we can get stuck in a nasty cycle unless
-            // we call it through the timer here.
-            m_postLayoutTasksTimer.startOneShot(0_s);
-        }
-        if (needsLayout())
-            layout();
-    }
+    runOrSchedulePostLayoutTasks();
 
     InspectorInstrumentation::didLayout(cookie, *layoutRoot);
     DebugPageOverlays::didLayout(frame());
 }
+
+void FrameView::runOrSchedulePostLayoutTasks()
+{
+    if (m_postLayoutTasksTimer.isActive())
+        return;
+
+    if (isInChildFrameWithFrameFlattening()) {
+        // While flattening frames, we defer post layout tasks to avoid getting stuck in a cycle,
+        // except updateWidgetPositions() which is required to kick off subframe layout in certain cases.
+        if (!m_inPerformPostLayoutTasks)
+            updateWidgetPositions();
+        m_postLayoutTasksTimer.startOneShot(0_s);
+        return;
+    }
+
+    // If we are already in performPostLayoutTasks(), defer post layout tasks until after we return
+    // to avoid re-entrancy.
+    if (m_inPerformPostLayoutTasks) {
+        m_postLayoutTasksTimer.startOneShot(0_s);
+        return;
+    }
+
+    performPostLayoutTasks();
+    if (needsLayout()) {
+        // If performPostLayoutTasks() made us layout again, let's defer the tasks until after we return.
+        m_postLayoutTasksTimer.startOneShot(0_s);
+        layout();
+    }
+}
 
 bool FrameView::shouldDeferScrollUpdateAfterContentSizeChange()
 {

Source/WebCore/page/FrameView.h

@@ -688,6 +688,7 @@ class FrameView final : public ScrollView {
 
     void forceLayoutParentViewIfNeeded();
     void flushPostLayoutTasksQueue();
+    void runOrSchedulePostLayoutTasks();
     void performPostLayoutTasks();
     void autoSizeIfEnabled();