Revert of Pinch/Zoom Infrastructure & Plumbing CL

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 e5f0271c93ff9a36096094b24781b2076bb6fbbc..0684a9c51ae441f1d4c560a8c9dd07ddc16bb780 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -338,7 +338,12 @@
   sync_tree->set_background_color(background_color_);
   sync_tree->set_has_transparent_background(has_transparent_background_);
 
-  if (page_scale_layer_ && inner_viewport_scroll_layer_) {
+  sync_tree->FindRootScrollLayer();
+
+  // TODO(wjmaclean) For now, not all LTH clients will register viewports, so
+  // only set them when available..
+  if (page_scale_layer_) {
+    DCHECK(inner_viewport_scroll_layer_);
     sync_tree->SetViewportLayersFromIds(
         page_scale_layer_->id(),
         inner_viewport_scroll_layer_->id(),
@@ -1040,8 +1045,8 @@
   if (!root_layer_.get())
     return;
 
-  gfx::Vector2d inner_viewport_scroll_delta;
-  gfx::Vector2d outer_viewport_scroll_delta;
+  gfx::Vector2d root_scroll_delta;
+  Layer* root_scroll_layer = FindFirstScrollableLayer(root_layer_.get());
 
   for (size_t i = 0; i < info.scrolls.size(); ++i) {
     Layer* layer =
@@ -1049,87 +1054,29 @@
                                                 info.scrolls[i].layer_id);
     if (!layer)
       continue;
-    if (layer == outer_viewport_scroll_layer_.get()) {
-      outer_viewport_scroll_delta += info.scrolls[i].scroll_delta;
-    } else if (layer == inner_viewport_scroll_layer_.get()) {
-      inner_viewport_scroll_delta += info.scrolls[i].scroll_delta;
+    if (layer == root_scroll_layer) {
+      root_scroll_delta += info.scrolls[i].scroll_delta;
     } else {
       layer->SetScrollOffsetFromImplSide(layer->scroll_offset() +
                                          info.scrolls[i].scroll_delta);
     }
   }
 
-  if (!inner_viewport_scroll_delta.IsZero() ||
-      !outer_viewport_scroll_delta.IsZero() ||
-      info.page_scale_delta != 1.f) {
+  if (!root_scroll_delta.IsZero() || info.page_scale_delta != 1.f) {
     // SetScrollOffsetFromImplSide above could have destroyed the tree,
     // so re-get this layer before doing anything to it.
+    root_scroll_layer = FindFirstScrollableLayer(root_layer_.get());
 
     // 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_);  // We should always have this.
-
-    inner_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
-        inner_viewport_scroll_layer_->scroll_offset() +
-        inner_viewport_scroll_delta);
-    if (outer_viewport_scroll_layer_) {
-      outer_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
-          outer_viewport_scroll_layer_->scroll_offset() +
-          outer_viewport_scroll_delta);
+    if (root_scroll_layer) {
+      root_scroll_layer->SetScrollOffsetFromImplSide(
+          root_scroll_layer->scroll_offset() + root_scroll_delta);
     }
     ApplyPageScaleDeltaFromImplSide(info.page_scale_delta);
-
-    client_->ApplyScrollAndScale(
-        inner_viewport_scroll_delta + outer_viewport_scroll_delta,
-        info.page_scale_delta);
-  }
-}
-
-gfx::Vector2d LayerTreeHost::DistributeScrollOffsetToViewports(
-    const gfx::Vector2d offset,
-    Layer* layer) {
-  DCHECK(layer);
-  if (layer != outer_viewport_scroll_layer_.get())
-    return offset;
-
-  gfx::Vector2d inner_viewport_offset =
-      inner_viewport_scroll_layer_->scroll_offset();
-  gfx::Vector2d outer_viewport_offset =
-      outer_viewport_scroll_layer_->scroll_offset();
-
-  if (offset == inner_viewport_offset + outer_viewport_offset) {
-    // In this case, nothing should change, so we just return to the outer
-    // viewport the offset is already has.
-    return outer_viewport_offset;
-  }
-
-  // In the spirit of document-scrolls-first, we always want any change to
-  // go to the outer viewport first.
-  gfx::Vector2d max_outer_viewport_scroll_offset =
-      outer_viewport_scroll_layer_->MaxScrollOffset();
-#if ENABLE_DCHECK
-// TODO(wjmaclean) The DCHECK below is triggering during zoom-out.
-// crbug.com/336574
-/*
-  gfx::Vector2d maxInnerViewportScrollOffset =
-      inner_viewport_scroll_layer_->MaxScrollOffset();
-
-  gfx::Vector2d totalMaxScrollOffset =
-      max_outer_viewport_scroll_offset + maxInnerViewportScrollOffset;
-  DCHECK(totalMaxScrollOffset.x() >= offset.x() &&
-         totalMaxScrollOffset.y() >= offset.y());
-*/
-#endif
-
-  outer_viewport_offset = offset - inner_viewport_offset;
-  outer_viewport_offset.SetToMin(max_outer_viewport_scroll_offset);
-  outer_viewport_offset.SetToMax(gfx::Vector2d());
-
-  inner_viewport_offset = offset - outer_viewport_offset;
-  inner_viewport_scroll_layer_->SetScrollOffset(inner_viewport_offset);
-
-  return outer_viewport_offset;
+    client_->ApplyScrollAndScale(root_scroll_delta, info.page_scale_delta);
+  }
 }
 
 void LayerTreeHost::StartRateLimiter() {