Remove dead code

Change-Id: I7e169b86c66e8c3ab5f4fd3b96ceed1d01c5a309
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643055
Auto-Submit: Stefan Zager <szager@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846150}

third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc

@@ -319,14 +319,6 @@ void PaintLayerCompositor::UpdateAssignmentsIfNeeded(
       update_type = std::max(update_type, kCompositingUpdateRebuildTree);
   }
 
-  GraphicsLayer* current_parent = nullptr;
-  // Save off our current parent. We need this in subframes, because our
-  // parent attached us to itself via AttachFrameContentLayersToIframeLayer().
-  if (!IsMainFrame() && update_root->GetCompositedLayerMapping()) {
-    current_parent =
-        update_root->GetCompositedLayerMapping()->MainGraphicsLayer()->Parent();
-  }
-
 #if DCHECK_IS_ON()
   if (update_root->GetCompositingState() != kPaintsIntoOwnBacking) {
     AssertWholeTreeNotComposited(*update_root);