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

mojo/examples/compositor_app/compositor_host.cc

Index: mojo/examples/compositor_app/compositor_host.cc
diff --git a/mojo/examples/compositor_app/compositor_host.cc b/mojo/examples/compositor_app/compositor_host.cc
index 90d04bbd6dddb74495eaa5ee5946ca29d9c75b37..306f3fdde72d1250a77782b9b800b7d5892854a7 100644
--- a/mojo/examples/compositor_app/compositor_host.cc
+++ b/mojo/examples/compositor_app/compositor_host.cc
@@ -72,6 +72,10 @@ void CompositorHost::BeginMainFrame(const cc::BeginFrameArgs& args) {
 }
 
 void CompositorHost::Layout() {}
+void CompositorHost::ApplyViewportDeltas(const gfx::Vector2d& inner_delta,
+                                         const gfx::Vector2d& outer_delta,
+                                         float page_scale,
+                                         float top_controls_delta) {}
 void CompositorHost::ApplyViewportDeltas(const gfx::Vector2d& scroll_delta,
                                          float page_scale,
                                          float top_controls_delta) {}