Bug 1166382 - Use the adjusted full zoom in nsDocument::GetViewportInfo(). r=tn

--HG--
extra : source : 13d43f2b9bc95018f5ed419a2649f0e5736029c8

dom/base/nsDocument.cpp

@@ -7879,7 +7879,11 @@ nsDocument::GetViewportInfo(const ScreenIntSize& aDisplaySize)
   // Compute the CSS-to-LayoutDevice pixel scale as the product of the
   // widget scale and the full zoom.
   nsPresContext* context = mPresShell->GetPresContext();
-  float fullZoom = context ? context->GetFullZoom() : 1.0;
+  // When querying the full zoom, get it from the device context rather than
+  // directly from the pres context, because the device context's value can
+  // include an adjustment necessay to keep the number of app units per device
+  // pixel an integer, and we want the adjusted value.
+  float fullZoom = context ? context->DeviceContext()->GetFullZoom() : 1.0;
   fullZoom = (fullZoom == 0.0) ? 1.0 : fullZoom;
   nsIWidget *widget = nsContentUtils::WidgetForDocument(this);
   float widgetScale = widget ? widget->GetDefaultScale().scale : 1.0f;