WorkspaceLayoutManager backdrop should fill entire region.

ash/wm/maximize_mode/workspace_backdrop_delegate.cc

Index: ash/wm/maximize_mode/workspace_backdrop_delegate.cc
diff --git a/ash/wm/maximize_mode/workspace_backdrop_delegate.cc b/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
index afa70052550bf39543cbde107be116f459bb5aa3..14c5daf875f4476f052cef8d081c35276128cd76 100644
--- a/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
+++ b/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
@@ -91,6 +91,10 @@ void WorkspaceBackdropDelegate::OnPostWindowStateTypeChange(
   RestackBackdrop();
 }
 
+void WorkspaceBackdropDelegate::OnDisplayWorkAreaInsetsChanged() {
+  AdjustToContainerBounds();
+}
+
 void WorkspaceBackdropDelegate::RestackBackdrop() {
   // Avoid recursive calls.
   if (in_restacking_)