CustomButton: restrict animation repaints to buttons that actually animate

ui/views/controls/button/md_text_button.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/controls/button/md_text_button.h"
 
 #include "base/i18n/case_conversion.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/color_palette.h"
@@ skipping 73 matching lines @@
 
   is_prominent_ = is_prominent;
   UpdateColors();
 }
 
 void MdTextButton::SetBgColorOverride(const base::Optional<SkColor>& color) {
   bg_color_override_ = color;
   UpdateColors();
 }
 
+void MdTextButton::OnPaintBackground(gfx::Canvas* canvas) {
+  LabelButton::OnPaintBackground(canvas);
+  if (hover_animation().is_animating() || state() == STATE_HOVERED) {
+    const int kHoverAlpha = is_prominent_ ? 0x0c : 0x05;
+    SkScalar alpha = hover_animation().CurrentValueBetween(0, kHoverAlpha);
+    canvas->FillRect(GetLocalBounds(), SkColorSetA(SK_ColorBLACK, alpha));
+  }
+}
+
 void MdTextButton::OnFocus() {
   LabelButton::OnFocus();
   FocusRing::Install(this);
 }
 
 void MdTextButton::OnBlur() {
   LabelButton::OnBlur();
   FocusRing::Uninstall(this);
 }
 
@@ skipping 81 matching lines @@
                                             : InkDropMode::OFF);
   set_has_ink_drop_action_on_click(true);
   SetHorizontalAlignment(gfx::ALIGN_CENTER);
   SetFocusForPlatform();
   SetMinSize(gfx::Size(kMinWidth, 0));
   SetFocusPainter(nullptr);
   label()->SetAutoColorReadabilityEnabled(false);
   set_request_focus_on_press(false);
   LabelButton::SetFontList(GetMdFontList());
 
+  set_animates_hover(true);
+
   // Paint to a layer so that the canvas is snapped to pixel boundaries (useful
   // for fractional DSF).
   SetPaintToLayer(true);
   layer()->SetFillsBoundsOpaquely(false);
 }
 
 MdTextButton::~MdTextButton() {}
 
 void MdTextButton::UpdatePadding() {
   // Don't use font-based padding when there's no text visible.
@@ skipping 67 matching lines @@
 
   SkColor stroke_color =
       is_prominent_ ? SK_ColorTRANSPARENT : SkColorSetA(text_color, 0x33);
   DCHECK_EQ(SK_AlphaOPAQUE, static_cast<int>(SkColorGetA(bg_color)));
   set_background(Background::CreateBackgroundPainter(
       true, Painter::CreateRoundRectWith1PxBorderPainter(
                 bg_color, stroke_color, kInkDropSmallCornerRadius)));
 }
 
 }  // namespace views