Only support left/right maximizing at 50% width when the --ash-enable-alternate-caption-button

ash/wm/workspace/workspace_window_resizer.cc

Index: ash/wm/workspace/workspace_window_resizer.cc
diff --git a/ash/wm/workspace/workspace_window_resizer.cc b/ash/wm/workspace/workspace_window_resizer.cc
index 4b8c0aaf7e9366f91aa1fd1bf6f8d88f9429b0c9..c68ad911556a8fb415815edb1fe998b067d640f6 100644
--- a/ash/wm/workspace/workspace_window_resizer.cc
+++ b/ash/wm/workspace/workspace_window_resizer.cc
@@ -422,8 +422,7 @@ void WorkspaceWindowResizer::CompleteDrag(int event_flags) {
                                initial_bounds :
                                details_.restore_bounds);
     }
-    window()->SetBounds(snap_sizer_->target_bounds());
-    return;
+    snap_sizer_->Snap();
   }
 }
 
@@ -855,7 +854,7 @@ void WorkspaceWindowResizer::UpdateSnapPhantomWindow(const gfx::Point& location,
   if (!did_move_or_resize_ || details_.window_component != HTCAPTION)
     return;
 
-  if (!wm::CanSnapWindow(window()))
+  if (!SnapSizer::CanSnapWindow(window()))
     return;
 
   if (window()->type() == aura::client::WINDOW_TYPE_PANEL &&
@@ -877,7 +876,7 @@ void WorkspaceWindowResizer::UpdateSnapPhantomWindow(const gfx::Point& location,
     snap_sizer_.reset(new SnapSizer(window(),
                                     location,
                                     edge,
-                                    internal::SnapSizer::OTHER_INPUT));
+                                    SnapSizer::STEP_YES));
   } else {
     snap_sizer_->Update(location);
   }