Fix for pinch virtual viewport flag wasn't fully enabled.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 3a12e982994ffc892394ea7769be20583993200a..6ac6a30933209d860e08d95341b659868ef26345 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -187,8 +187,12 @@ scoped_ptr<RenderWidgetCompositor> RenderWidgetCompositor::Create(
         settings.top_controls_hide_threshold = hide_threshold;
   }
 
+#if defined(OS_CHROMEOS)
+  settings.use_pinch_virtual_viewport = true;
+#else
   settings.use_pinch_virtual_viewport =
       cmd->HasSwitch(cc::switches::kEnablePinchVirtualViewport);
+#endif

[piman, 2014/04/25 20:53:05]

I would prefer if this kind of per-platform decision was in one place, in the
browser, rather than littered all over the code, with different logic - as this
CL shows, it's easy to miss one place and have the wrong behavior.

See for example what we do for IsThreadedCompositingEnabled or
IsDelegatedRendererEnabled or IsImplSidePaintingEnabled etc. in
content/browser/gpu/compositor_util.cc

We have one single place that makes the decision, and then this decision is used
on the browser side, and passed (as a command line flag, for lack of better way)
to the renderer. We can even test that logic.

I think we should be able to easily add a IsPinchVirtualViewportEnabled in
compositor_util.cc, with all the logic there, and use that information to pass a
single enable flag to the renderer (see render_process_host_impl.cc) and use
that flag to make all the decisions.

   settings.allow_antialiasing &=
       !cmd->HasSwitch(cc::switches::kDisableCompositedAntialiasing);
 
@@ -289,7 +293,7 @@ scoped_ptr<RenderWidgetCompositor> RenderWidgetCompositor::Create(
   if (ui::IsOverlayScrollbarEnabled()) {
     settings.scrollbar_animator = cc::LayerTreeSettings::Thinning;
     settings.solid_color_scrollbar_color = SkColorSetARGB(128, 128, 128, 128);
-  } else if (cmd->HasSwitch(cc::switches::kEnablePinchVirtualViewport)) {
+  } else if (settings.use_pinch_virtual_viewport) {
     // use_pinch_zoom_scrollbars is only true on desktop when non-overlay
     // scrollbars are in use.
     settings.use_pinch_zoom_scrollbars = true;