[DevTools] Use device metrics emulation implemented in content.

Source/core/page/FrameView.cpp

Index: Source/core/page/FrameView.cpp
diff --git a/Source/core/page/FrameView.cpp b/Source/core/page/FrameView.cpp
index 26a418a8b757791bdc66d9f80c07dbea17c435c8..ad75cb86228ed473d524607a449b18cd119267f4 100644
--- a/Source/core/page/FrameView.cpp
+++ b/Source/core/page/FrameView.cpp
@@ -181,6 +181,7 @@ FrameView::FrameView(Frame* frame)
     , m_didRunAutosize(false)
     , m_hasSoftwareFilters(false)
     , m_visibleContentScaleFactor(1)
+    , m_inputEventsScaleFactorForEmulation(1)
     , m_partialLayout()
 {
     ASSERT(m_frame);
@@ -2554,6 +2555,15 @@ void FrameView::setVisibleContentScaleFactor(float visibleContentScaleFactor)
     updateScrollbars(scrollOffset());
 }
 
+void FrameView::setInputEventsScaleFactorForEmulation(float contentScaleFactor)
+{
+    if (m_inputEventsScaleFactorForEmulation == contentScaleFactor)
+        return;
+
+    m_inputEventsScaleFactorForEmulation = contentScaleFactor;
+    updateScrollbars(scrollOffset());
+}
+
 bool FrameView::scrollbarsCanBeActive() const
 {
     if (m_frame->view() != this)