CrOS Shelf: Set maximized shelf color to be completely opaque

TBR=oshima@chromium.org

Bug: 1052441, 1022544
Change-Id: Ifc0399af5c8d4f32322b685161d8fea2aa6867fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067797Reviewed-by: Matthew Mourgos <mmourgos@chromium.org>
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744108}

ash/shelf/shelf_config.cc

@@ -322,10 +322,7 @@ SkColor ShelfConfig::GetShelfWithAppListColor() const {
 }
 
 SkColor ShelfConfig::GetMaximizedShelfColor() const {
-  // Using 0xFF causes clipping on the overlay candidate content, which prevent
-  // HW overlay, probably due to a bug in compositor. Fix it and use 0xFF.
-  // crbug.com/901538
-  return SkColorSetA(GetDefaultShelfColor(), 254);  // ~100% opacity
+  return SkColorSetA(GetDefaultShelfColor(), 0xFF);  // 100% opacity
 }
 
 SkColor ShelfConfig::GetThemedColorFromWallpaper(SkColor base_color) const {