GCC: SizeBounds setters cannot be constexpr

As base::Optional move assignment operator is not constexpr, the
setters using it cannot be constexpr either.

Bug: 819294
Change-Id: I0c6e0325728f05ff9d6d892a3508ebb1b21a85c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2041611Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Commit-Queue: José Dapena Paz <jdapena@igalia.com>
Cr-Commit-Position: refs/heads/master@{#742834}

ui/views/layout/layout_types.h

@@ -45,14 +45,10 @@ class VIEWS_EXPORT SizeBounds {
   ~SizeBounds() = default;
 
   constexpr const base::Optional<int>& width() const { return width_; }
-  constexpr void set_width(base::Optional<int> width) {
-    width_ = std::move(width);
-  }
+  void set_width(base::Optional<int> width) { width_ = std::move(width); }
 
   constexpr const base::Optional<int>& height() const { return height_; }
-  constexpr void set_height(base::Optional<int> height) {
-    height_ = std::move(height);
-  }
+  void set_height(base::Optional<int> height) { height_ = std::move(height); }
 
   constexpr bool is_fully_bounded() const { return width_ && height_; }