Reland "Avoid layout/full-repaint on view height change if possible"

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 7746f348bf0c895e4966c9ba283bd36ddec8831a..283d7901c6818960293fe2e1c833ea749f9a458e 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -3179,8 +3179,42 @@ void FrameView::setLayoutSizeInternal(const IntSize& size)
     if (m_layoutSize == size)
         return;
 
+    bool widthChanged = m_layoutSize.width() != size.width();
     m_layoutSize = size;
-    contentsResized();
+
+    // Update scrollbars. Not calling this->contentsResized() to avoid setNeedsLayout.
+    ScrollView::contentsResized();
+
+    RenderView* renderView = this->renderView();
+    if (!renderView)
+        return;
+
+    // If needsLayout, the next layout will do all the things required on layoutSize change.
+    if (renderView->needsLayout())
+        return;
+
+    if (widthChanged) {
+        setNeedsLayout();
+        return;
+    }
+
+    performPreLayoutTasks();
+
+    // During pre-layout tasks, viewport media queries, viewport sizes and others may cause
+    // style update and set needsLayout flag.
+    if (renderView->needsLayout())
+        return;
+
+    if (!renderView->trySimplifiedLayoutOnHeightChange()) {
+        setNeedsLayout();
+        return;
+    }
+
+    // RenderView has finished a simplified layout for the height change. We need to perform
+    // necessary post-layout tasks for the simplified layout.
+    scheduleOrPerformPostLayoutTasks();
+    if (frame().page())
+        frame().page()->chrome().client().layoutUpdated(m_frame.get());
 }
 
 void FrameView::didAddScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)