Adds scroll position/scale emulation to DevTools.

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

Index: third_party/WebKit/Source/core/frame/VisualViewport.cpp
diff --git a/third_party/WebKit/Source/core/frame/VisualViewport.cpp b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
index fe5ac4494ee2ecb6dc58e36d675b0f7f4d2dad20..ee67ea1d5703b2fcf3bcd89a4f2533b4fd2440aa 100644
--- a/third_party/WebKit/Source/core/frame/VisualViewport.cpp
+++ b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
@@ -36,6 +36,7 @@
 #include "core/frame/LocalFrame.h"
 #include "core/frame/PageScaleConstraints.h"
 #include "core/frame/PageScaleConstraintsSet.h"
+#include "core/frame/ScrollAndScaleEmulator.h"
 #include "core/frame/Settings.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/layout/TextAutosizer.h"
@@ -222,6 +223,12 @@ void VisualViewport::setScale(float scale)
     setScaleAndLocation(scale, m_offset);
 }
 
+void VisualViewport::setScrollAndScaleEmulator(const RefPtr<ScrollAndScaleEmulator>& emulator)
+{
+    m_scrollAndScaleEmulator = emulator;
+    setScaleAndLocation(scale(), location());

[bokan, 2016/07/01 21:05:12]

We should call setScaleAndLocation to clamp the scroll position from the caller
(inside ScrollAndScaleEmulator). Also, visual viewport has a clampToBoundaries
method you could use.

[Eric Seckler, 2016/07/04 14:33:08]

Done, using clampToBoundaries() now. (This boils down to the same
setScaleAndLocation() invocation.)

+}
+
 double VisualViewport::scrollLeft()
 {
     if (!mainFrame())
@@ -550,7 +557,23 @@ int VisualViewport::scrollSize(ScrollbarOrientation orientation) const
 
 IntPoint VisualViewport::minimumScrollPosition() const
 {
-    return IntPoint();
+    return flooredIntPoint(minimumScrollPositionDouble());
+}
+
+DoublePoint VisualViewport::minimumScrollPositionDouble() const
+{
+    if (m_scrollAndScaleEmulator) {
+        DoublePoint minimum = calculateMinimumScrollPositionDouble();
+        DoublePoint maximum = calculateMaximumScrollPositionDouble();
+        return m_scrollAndScaleEmulator->applyVisualViewportPositionOverride(minimum, minimum, maximum);
+    }
+
+    return calculateMinimumScrollPositionDouble();
+}
+
+DoublePoint VisualViewport::calculateMinimumScrollPositionDouble() const
+{
+    return DoublePoint();
 }
 
 IntPoint VisualViewport::maximumScrollPosition() const
@@ -560,6 +583,17 @@ IntPoint VisualViewport::maximumScrollPosition() const
 
 DoublePoint VisualViewport::maximumScrollPositionDouble() const
 {
+    if (m_scrollAndScaleEmulator) {
+        DoublePoint minimum = calculateMinimumScrollPositionDouble();
+        DoublePoint maximum = calculateMaximumScrollPositionDouble();
+        return m_scrollAndScaleEmulator->applyVisualViewportPositionOverride(maximum, minimum, maximum);
+    }
+
+    return calculateMaximumScrollPositionDouble();
+}
+
+DoublePoint VisualViewport::calculateMaximumScrollPositionDouble() const
+{
     if (!mainFrame())
         return IntPoint();