Adds scroll position/scale emulation to DevTools.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 26 matching lines @@
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/RenderedPosition.h"
 #include "core/editing/markers/DocumentMarkerController.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/frame/EventHandlerRegistry.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Location.h"
 #include "core/frame/PageScaleConstraintsSet.h"
+#include "core/frame/ScrollAndScaleEmulator.h"
 #include "core/frame/Settings.h"
 #include "core/frame/TopControls.h"
 #include "core/frame/VisualViewport.h"
 #include "core/html/HTMLFrameElement.h"
 #include "core/html/HTMLPlugInElement.h"
 #include "core/html/HTMLTextFormControlElement.h"
 #include "core/html/parser/TextResourceDecoder.h"
 #include "core/input/EventHandler.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/inspector/InspectorTraceEvents.h"
@@ skipping 141 matching lines @@
 
 DEFINE_TRACE(FrameView)
 {
     visitor->trace(m_frame);
     visitor->trace(m_fragmentAnchor);
     visitor->trace(m_scrollableAreas);
     visitor->trace(m_animatingScrollableAreas);
     visitor->trace(m_autoSizeInfo);
     visitor->trace(m_horizontalScrollbar);
     visitor->trace(m_verticalScrollbar);
+    visitor->trace(m_scrollAndScaleEmulator);
     visitor->trace(m_children);
     visitor->trace(m_viewportScrollableArea);
     visitor->trace(m_scrollAnchor);
     Widget::trace(visitor);
     ScrollableArea::trace(visitor);
 }
 
 void FrameView::reset()
 {
     m_hasPendingLayout = false;
@@ skipping 1376 matching lines @@
     DoublePoint newScrollPosition = clampScrollPosition(scrollPoint);
     if (newScrollPosition == scrollPositionDouble())
         return;
 
     if (scrollBehavior == ScrollBehaviorAuto)
         scrollBehavior = scrollBehaviorStyle();
 
     ScrollableArea::setScrollPosition(newScrollPosition, scrollType, scrollBehavior);
 }
 
+void FrameView::setScrollAndScaleEmulator(ScrollAndScaleEmulator* emulator)
+{
+    m_scrollAndScaleEmulator = emulator;
+    setScrollPosition(scrollPosition(), ProgrammaticScroll, ScrollBehaviorInstant);
+}
+
 void FrameView::didUpdateElasticOverscroll()
 {
     Page* page = frame().page();
     if (!page)
         return;
     FloatSize elasticOverscroll = page->chromeClient().elasticOverscroll();
     if (m_horizontalScrollbar) {
         float delta = elasticOverscroll.width() - m_horizontalScrollbar->elasticOverscroll();
         if (delta != 0) {
             m_horizontalScrollbar->setElasticOverscroll(elasticOverscroll.width());
@@ skipping 1586 matching lines @@
     ScrollableArea::didAddScrollbar(scrollbar, orientation);
 }
 
 void FrameView::setTopControlsViewportAdjustment(float adjustment)
 {
     m_topControlsViewportAdjustment = adjustment;
 }
 
 IntPoint FrameView::maximumScrollPosition() const
 {
+    IntPoint minimum = calculateMinimumScrollPosition();
+    IntPoint maximum = calculateMaximumScrollPosition().expandedTo(minimum);
+
+    if (m_scrollAndScaleEmulator)
+        return m_scrollAndScaleEmulator->applyFramePositionOverride(maximum).shrunkTo(maximum).expandedTo(minimum);

[dgozman, 2016/07/21 20:54:08]

Is this web-observable? E.g. what this snippet will produce when override is on?

body.scrollTop = 100;
console.log(body.scrollTop);

If it's observable, we break the web contract. I'm not sure that's good.

[Eric Seckler, 2016/07/22 14:44:48]

For the layout viewport (frame), the change of scroll position through the
override is observable by the page (again, we want that). The page won't be able
to change the position, though. So in your example, assuming overriden scroll
position is (0, 0):

body.scrollTop = 100; // Will be clamped to 0, so no change in position.
console.log(body.scrollTop); // Will log 0.

I'm not sure if this really breaks contracts, since setting body.scrollTop
outside min/max generally also clamps. We're just enforcing a different min/max,
which I'd argue is in the user-agent's right.

+
+    return maximum;
+}
+
+IntPoint FrameView::calculateMaximumScrollPosition() const
+{
     // Make the same calculation as in CC's LayerImpl::MaxScrollOffset()
     // FIXME: We probably shouldn't be storing the bounds in a float. crbug.com/422331.
     IntSize visibleSize = visibleContentSize(ExcludeScrollbars) + topControlsSize();
     IntSize contentBounds = contentsSize();
     IntPoint maximumPosition = -scrollOrigin() + (contentBounds - visibleSize);
-    return maximumPosition.expandedTo(minimumScrollPosition());
+    return maximumPosition;
 }
 
 void FrameView::addChild(Widget* child)
 {
     ASSERT(child != this && !child->parent());
     child->setParent(this);
     m_children.add(child);
 }
 
 void FrameView::setHasHorizontalScrollbar(bool hasBar)
@@ skipping 98 matching lines @@
     return IntRect(flooredIntPoint(m_scrollPosition), visibleContentSize(scrollbarInclusion));
 }
 
 IntSize FrameView::contentsSize() const
 {
     return m_contentsSize;
 }
 
 IntPoint FrameView::minimumScrollPosition() const
 {
+    IntPoint minimum = calculateMinimumScrollPosition();
+    IntPoint maximum = calculateMaximumScrollPosition().expandedTo(minimum);
+
+    if (m_scrollAndScaleEmulator)
+        return m_scrollAndScaleEmulator->applyFramePositionOverride(minimum).shrunkTo(maximum).expandedTo(minimum);
+
+    return minimum;
+}
+
+IntPoint FrameView::calculateMinimumScrollPosition() const
+{
     return IntPoint(-scrollOrigin().x(), -scrollOrigin().y());
 }
 
 void FrameView::adjustScrollbarOpacity()
 {
     if (m_horizontalScrollbar && layerForHorizontalScrollbar()) {
         bool isOpaqueScrollbar = !m_horizontalScrollbar->isOverlayScrollbar();
         layerForHorizontalScrollbar()->setContentsOpaque(isOpaqueScrollbar);
     }
     if (m_verticalScrollbar && layerForVerticalScrollbar()) {
@@ skipping 942 matching lines @@
 }
 
 bool FrameView::canThrottleRendering() const
 {
     if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
         return false;
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 } // namespace blink