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

ash/wm/gestures/system_pinch_handler.cc

Index: ash/wm/gestures/system_pinch_handler.cc
diff --git a/ash/wm/gestures/system_pinch_handler.cc b/ash/wm/gestures/system_pinch_handler.cc
index a0f5d12e00b04642df7a0f6a552d6e5dd80ac397..e90a21f47f85dba88b18abbeedb548b2e8d53ac0 100644
--- a/ash/wm/gestures/system_pinch_handler.cc
+++ b/ash/wm/gestures/system_pinch_handler.cc
@@ -86,14 +86,18 @@ SystemGestureStatus SystemPinchHandler::ProcessGestureEvent(
 
       if (event.details().swipe_left() || event.details().swipe_right()) {
         // Snap for left/right swipes.
-        ui::ScopedLayerAnimationSettings settings(
-            target_->layer()->GetAnimator());
-        internal::SnapSizer::SnapWindow(target_,
-            event.details().swipe_left() ? internal::SnapSizer::LEFT_EDGE :
-                                           internal::SnapSizer::RIGHT_EDGE);
+        using internal::SnapSizer;
+        if (SnapSizer::CanSnapWindow(target_)) {
+          ui::ScopedLayerAnimationSettings settings(
+              target_->layer()->GetAnimator());
+          SnapSizer::Edge edge = event.details().swipe_left() ?
+              SnapSizer::LEFT_EDGE : SnapSizer::RIGHT_EDGE;
+          SnapSizer::SnapWindow(target_, edge, SnapSizer::STEP_NO);
+        }
       } else if (event.details().swipe_up()) {
         if (!wm::IsWindowMaximized(target_) &&
-            !wm::IsWindowFullscreen(target_))
+            !wm::IsWindowFullscreen(target_) &&
+            wm::CanMaximizeWindow(target_))
           wm::MaximizeWindow(target_);
       } else if (event.details().swipe_down()) {
         wm::MinimizeWindow(target_);