Adds scroll position/scale emulation to DevTools.

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

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 687b58d8451b0789bb81f5d439dc29cfbdc80004..f3f41a642112ed7e9d92dfc841c834f15d8e95ba 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -44,6 +44,7 @@
 #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"
@@ -205,6 +206,7 @@ DEFINE_TRACE(FrameView)
     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);
@@ -1601,6 +1603,12 @@ void FrameView::setScrollPosition(const DoublePoint& scrollPoint, ScrollType scr
     ScrollableArea::setScrollPosition(newScrollPosition, scrollType, scrollBehavior);
 }
 
+void FrameView::setScrollAndScaleEmulator(ScrollAndScaleEmulator* emulator)
+{
+    m_scrollAndScaleEmulator = emulator;
+    setScrollPosition(scrollPosition(), ProgrammaticScroll, ScrollBehaviorInstant);
+}
+
 void FrameView::didUpdateElasticOverscroll()
 {
     Page* page = frame().page();
@@ -3207,12 +3215,23 @@ void FrameView::setTopControlsViewportAdjustment(float 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)
@@ -3331,6 +3350,17 @@ IntSize FrameView::contentsSize() const
 
 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());
 }