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

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index eed1e5a7e151e74942e0b78d54b96f38a2f2874d..38795bb3c1698f8565bd0b53014cf347508d58ff 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1091,11 +1091,11 @@ void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
     // SetScrollOffsetFromImplSide above could have destroyed the tree,
     // so re-get this layer before doing anything to it.
 
+    DCHECK(inner_viewport_scroll_layer_.get());  // We should always have this.
+
     // Preemptively apply the scroll offset and scale delta here before sending
     // it to the client.  If the client comes back and sets it to the same
     // value, then the layer can early out without needing a full commit.
-    DCHECK(inner_viewport_scroll_layer_.get());  // We should always have this.
-
     inner_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
         inner_viewport_scroll_layer_->scroll_offset() +
         inner_viewport_scroll_delta);
@@ -1104,12 +1104,20 @@ void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
           outer_viewport_scroll_layer_->scroll_offset() +
           outer_viewport_scroll_delta);
     }
-    ApplyPageScaleDeltaFromImplSide(info->page_scale_delta);
 
-    client_->ApplyViewportDeltas(
-        inner_viewport_scroll_delta + outer_viewport_scroll_delta,
-        info->page_scale_delta,
-        info->top_controls_delta);
+    ApplyPageScaleDeltaFromImplSide(info->page_scale_delta);
+    if (!outer_viewport_scroll_layer_.get()) {
+      client_->ApplyViewportDeltas(
+          inner_viewport_scroll_delta + outer_viewport_scroll_delta,
+          info->page_scale_delta,
+          info->top_controls_delta);
+    } else {
+      client_->ApplyViewportDeltas(
+          inner_viewport_scroll_delta,
+          outer_viewport_scroll_delta,
+          info->page_scale_delta,
+          info->top_controls_delta);
+    }
   }
 }