Fix white paint artifacts around holding space images.

Before: http://shortn/_L6D4o1zrki
After: http://shortn/_MuXhA5lF6T

Bug: 1163326
Change-Id: Ifed54414f0adfabc289d9f90f665226a7300d099
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2612050
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840429}

ash/system/holding_space/holding_space_drag_util.cc

@@ -155,12 +155,18 @@ class DragImageItemView : public views::View {
   }
 
   void OnPaintBackground(gfx::Canvas* canvas) override {
+    // NOTE: The contents bounds are shrunk by a single pixel to avoid
+    // painting the background outside content bounds as might otherwise occur
+    // due to pixel rounding. Failure to do so could result in white paint
+    // artifacts.
+    gfx::Rect bounds(GetContentsBounds());
+    bounds.Inset(gfx::Insets(1));
+
     cc::PaintFlags flags;
     flags.setAntiAlias(true);
     flags.setColor(SK_ColorWHITE);
     flags.setLooper(gfx::CreateShadowDrawLooper(GetShadowDetails().values));
-    canvas->DrawRoundRect(GetContentsBounds(), kDragImageItemViewCornerRadius,
-                          flags);
+    canvas->DrawRoundRect(bounds, kDragImageItemViewCornerRadius, flags);
   }
 
  private:

ash/system/holding_space/holding_space_tray_icon_preview.cc

@@ -313,12 +313,16 @@ void HoldingSpaceTrayIconPreview::OnPaintLayer(
   gfx::Canvas* canvas = recorder.canvas();
 
   // Background.
+  // NOTE: The background radius is shrunk by a single pixel to avoid being
+  // painted outside `contents_image_` bounds as might otherwise occur due to
+  // pixel rounding. Failure to do so could result in white paint artifacts.
   cc::PaintFlags flags;
   flags.setAntiAlias(true);
   flags.setColor(SK_ColorWHITE);
   canvas->DrawCircle(
       contents_bounds.CenterPoint(),
-      std::min(contents_bounds.width(), contents_bounds.height()) / 2, flags);
+      std::min(contents_bounds.width(), contents_bounds.height()) / 2 - 1,
+      flags);
 
   // Contents.
   if (!contents_image_.isNull()) {