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 711d891a824a3e2b9f7211905cd5df5c9b6ecc27..a6b90cfad46c57ec38b461fcbecc64f72e23817c 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -150,6 +150,7 @@ FrameView::FrameView(LocalFrame* frame)
     , m_verticalScrollbarMode(ScrollbarAuto)
     , m_horizontalScrollbarLock(false)
     , m_verticalScrollbarLock(false)
+    , m_scrollOverrideEnabled(false)
     , m_scrollbarsAvoidingResizer(0)
     , m_scrollbarsSuppressed(false)
     , m_inUpdateScrollbars(false)
@@ -1564,7 +1565,7 @@ void FrameView::clearFragmentAnchor()
 
 void FrameView::setScrollPosition(const DoublePoint& scrollPoint, ScrollType scrollType, ScrollBehavior scrollBehavior)
 {
-    DoublePoint newScrollPosition = clampScrollPosition(scrollPoint);
+    DoublePoint newScrollPosition = clampScrollPosition(applyScrollOverrideToPosition(newScrollPosition));
     if (newScrollPosition == scrollPositionDouble())
         return;
 
@@ -1574,6 +1575,18 @@ void FrameView::setScrollPosition(const DoublePoint& scrollPoint, ScrollType scr
     ScrollableArea::setScrollPosition(newScrollPosition, scrollType, scrollBehavior);
 }
 
+void FrameView::setScrollOverride(const DoublePoint& position)
+{
+    m_scrollOverrideEnabled = true;
+    m_scrollOverridePosition = position;
+    setScrollPosition(scrollPosition(), ProgrammaticScroll, ScrollBehaviorInstant);
+}
+
+void FrameView::clearScrollOverride()
+{
+    m_scrollOverrideEnabled = false;
+}
+
 void FrameView::didUpdateElasticOverscroll()
 {
     Page* page = frame().page();
@@ -3233,7 +3246,7 @@ void FrameView::setScrollOffset(const DoublePoint& offset, ScrollType scrollType
 {
     // TODO(skobes): We shouldn't have to clamp here; instead we should update callers
     // ScrollableArea::scrollPositionChanged to only pass clamped offsets.
-    DoublePoint newPosition = clampScrollPosition(offset);
+    DoublePoint newPosition = clampScrollPosition(applyScrollOverrideToPosition(offset));
 
     DoublePoint oldPosition = m_scrollPosition;
     DoubleSize scrollDelta = newPosition - oldPosition;
@@ -3282,6 +3295,18 @@ void FrameView::setScrollOffset(const DoublePoint& offset, ScrollType scrollType
         m_scrollAnchor.clear();
 }
 
+DoublePoint FrameView::applyScrollOverrideToPosition(const DoublePoint& position)
+{
+    DoublePoint newPosition = position;
+    if (m_scrollOverrideEnabled) {
+        if (m_scrollOverridePosition.x() >= 0)

[Sami, 2016/06/23 17:34:03]

Do we need to validate the coordinates again here?

[Eric Seckler, 2016/06/23 18:12:43]

At the moment, I'm using a value <0 to signal "no override for this coordinate".
Does that make sense? If so, I will add a comment to that effect.

[Sami, 2016/06/24 14:48:26]

Oh I see, I didn't notice we can override just one axis. Hopefully this will be
more obvious in the new centralized class.

+            newPosition.setX(m_scrollOverridePosition.x());
+        if (m_scrollOverridePosition.y() >= 0)
+            newPosition.setY(m_scrollOverridePosition.y());
+    }
+    return newPosition;
+}
+
 void FrameView::windowResizerRectChanged()
 {
     updateScrollbars();