Made double-tap zoom work in pinch virtual viewport mode. (Blink-side)

Source/core/frame/PinchViewport.cpp

Index: Source/core/frame/PinchViewport.cpp
diff --git a/Source/core/frame/PinchViewport.cpp b/Source/core/frame/PinchViewport.cpp
index 8cb90bdf3d23ebd7d6c687171dd226e4d2e48d8c..d8bea70e8458612fe2e1ad344e6de7978970eca0 100644
--- a/Source/core/frame/PinchViewport.cpp
+++ b/Source/core/frame/PinchViewport.cpp
@@ -170,7 +170,7 @@ void PinchViewport::move(const FloatPoint& delta)
     setLocation(m_offset + delta);
 }
 
-void PinchViewport::setScale(float scale)
+void PinchViewport::setScaleWithoutClampingViewportOffset(float scale)
 {
     if (scale == m_scale)
         return;
@@ -185,13 +185,18 @@ void PinchViewport::setScale(float scale)
     if (!m_innerViewportScrollLayer)
         return;
 
-    // Ensure we clamp so we remain within the bounds.
-    setLocation(visibleRect().location());
-
     // TODO: We should probably be calling scaleDidChange type functions here.
     // see Page::setPageScaleFactor.
 }
 
+void PinchViewport::setScale(float scale)
+{
+    setScaleWithoutClampingViewportOffset(scale);
+
+    // Ensure we clamp so we remain within the bounds.
+    setLocation(visibleRect().location());
+}
+
 // Modifies the top of the graphics layer tree to add layers needed to support
 // the inner/outer viewport fixed-position model for pinch zoom. When finished,
 // the tree will look like this (with * denoting added layers):
@@ -351,6 +356,26 @@ IntPoint PinchViewport::maximumScrollPosition() const
     return flooredIntPoint(FloatSize(contentsSize()) - visibleRect().size());
 }
 
+IntPoint PinchViewport::clampDocumentOffsetAtScale(const IntPoint& offset, float scale)
+{
+    if (!mainFrame() || !mainFrame()->view())
+        return IntPoint();
+
+    FrameView* view = mainFrame()->view();
+
+    FloatSize scaledSize(m_size);
+    scaledSize.scale(1 / scale);
+
+    IntPoint pinchViewportMax = flooredIntPoint(FloatSize(contentsSize()) - scaledSize);
+    IntPoint max = view->maximumScrollPosition() + pinchViewportMax;
+    IntPoint min = view->minimumScrollPosition(); // PinchViewportMin should be (0, 0)
+
+    IntPoint clamped = offset;
+    clamped = clamped.shrunkTo(max);
+    clamped = clamped.expandedTo(min);
+    return clamped;
+}
+
 IntRect PinchViewport::scrollableAreaBoundingBox() const
 {
     // This method should return the bounding box in the parent view's coordinate