Fix static initializer in ambient_background_image_view.cc.

https://crrev.com/809702 added a global constant to
ambient_background_image_view.cc, but the constant adds a static
initializer. Avoid this by making the constant local to the method it is
used in. Then it is initialized on first use instead.

Bug: 537099
Change-Id: I1724e5a563e1a30a6aa6c8b306626ec86f6a570a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2427549Reviewed-by: Tao Wu <wutao@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810037}

ash/ambient/ui/ambient_background_image_view.cc

@@ -44,10 +44,6 @@ int translate_y_direction = -1;
 int current_x_translation = 0;
 int current_y_translation = 0;
 
-const views::FlexSpecification kUnboundedScaleToZero(
-    views::MinimumFlexSizeRule::kScaleToZero,
-    views::MaximumFlexSizeRule::kUnbounded);
-
 gfx::ImageSkia ResizeImage(const gfx::ImageSkia& image,
                            const gfx::Size& view_size) {
   if (image.isNull())
@@ -165,6 +161,10 @@ void AmbientBackgroundImageView::ResetRelatedImageForTesting() {
 }
 
 void AmbientBackgroundImageView::InitLayout() {
+  static const views::FlexSpecification kUnboundedScaleToZero(
+      views::MinimumFlexSizeRule::kScaleToZero,
+      views::MaximumFlexSizeRule::kUnbounded);
+
   SetLayoutManager(std::make_unique<views::FillLayout>());
 
   // Inits container for images.