Ensure find bar background is opaque

Bug: 918553
Change-Id: I03c20eedeede033bcfb912672ab29f02e8090c14
Reviewed-on: https://chromium-review.googlesource.com/c/1393532Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619641}

chrome/browser/ui/views/find_bar_view.cc

@@ -506,8 +506,10 @@ const char* FindBarView::GetClassName() const {
 }
 
 void FindBarView::OnNativeThemeChanged(const ui::NativeTheme* theme) {
-  SkColor bg_color = theme->GetSystemColor(
-      ui::NativeTheme::kColorId_TextfieldDefaultBackground);
+  SkColor bg_color =
+      SkColorSetA(theme->GetSystemColor(
+                      ui::NativeTheme::kColorId_TextfieldDefaultBackground),
+                  0xFF);
   auto border = std::make_unique<views::BubbleBorder>(
       views::BubbleBorder::NONE, views::BubbleBorder::SMALL_SHADOW, bg_color);
   SetBackground(std::make_unique<views::BubbleBackground>(border.get()));