nudges: Paint gradient background on view instead of using mask layer.

The view is quite large, so removing the mask will improve draw times
and use less GPU memory. Also changed the end gradient colour to match
the spec; personally I think using transparent as the end gradient
looked better.

Test: manual
Bug: 1056967
Change-Id: I254e11bca1a85c6bf19a74e8e5e852d00f568f15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079687Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745569}

ash/wm/gestures/back_gesture/back_gesture_contextual_nudge.cc

@@ -11,7 +11,6 @@
 #include "base/timer/timer.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/compositor/layer_animation_observer.h"
-#include "ui/compositor/paint_recorder.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/color_palette.h"
@@ -26,8 +25,10 @@ namespace {
 // Width of the contextual nudge.
 constexpr int kBackgroundWidth = 160;
 
-// Color of the contextual nudge.
-constexpr SkColor kBackgroundColor = SkColorSetA(SK_ColorBLACK, 153);  // 60%
+// Colors of the contextual nudge background gradient.
+constexpr SkColor kBackgroundStartColor =
+    SkColorSetA(SK_ColorBLACK, 153);  // 60%
+constexpr SkColor kBackgroundEndColor = SkColorSetARGB(0, 168, 168, 168);
 
 // Radius of the circle in the middle of the contextual nudge.
 constexpr int kCircleRadius = 20;
@@ -92,40 +93,6 @@ std::unique_ptr<views::Widget> CreateWidget() {
   return widget;
 }
 
-class GradientLayerDelegate : public ui::LayerDelegate {
- public:
-  GradientLayerDelegate() : layer_(ui::LAYER_TEXTURED) {
-    layer_.set_delegate(this);
-    layer_.SetFillsBoundsOpaquely(false);
-  }
-
-  ~GradientLayerDelegate() override { layer_.set_delegate(nullptr); }
-
-  ui::Layer* layer() { return &layer_; }
-
- private:
-  // ui::LayerDelegate:
-  void OnPaintLayer(const ui::PaintContext& context) override {
-    const gfx::Size size = layer()->size();
-    ui::PaintRecorder recorder(context, size);
-
-    cc::PaintFlags flags;
-    flags.setBlendMode(SkBlendMode::kSrc);
-    flags.setAntiAlias(false);
-    flags.setShader(
-        gfx::CreateGradientShader(gfx::Point(), gfx::Point(size.width(), 0),
-                                  SK_ColorBLACK, SK_ColorTRANSPARENT));
-    recorder.canvas()->DrawRect(gfx::Rect(gfx::Point(), size), flags);
-  }
-  void OnDeviceScaleFactorChanged(float old_device_scale_factor,
-                                  float new_device_scale_factor) override {}
-
-  ui::Layer layer_;
-
-  GradientLayerDelegate(const GradientLayerDelegate&) = delete;
-  GradientLayerDelegate& operator=(const GradientLayerDelegate&) = delete;
-};
-
 }  // namespace
 
 class BackGestureContextualNudge::ContextualNudgeView
@@ -133,15 +100,11 @@ class BackGestureContextualNudge::ContextualNudgeView
       public ui::ImplicitAnimationObserver {
  public:
   explicit ContextualNudgeView(base::OnceClosure callback)
-      : suggestion_view_(new SuggestionView(this)),
-        callback_(std::move(callback)) {
+      : callback_(std::move(callback)) {
     SetPaintToLayer();
     layer()->SetFillsBoundsOpaquely(false);
 
-    gradient_layer_delegate_ = std::make_unique<GradientLayerDelegate>();
-    layer()->SetMaskLayer(gradient_layer_delegate_->layer());
-
-    AddChildView(suggestion_view_);
+    suggestion_view_ = AddChildView(std::make_unique<SuggestionView>(this));
 
     show_timer_.Start(
         FROM_HERE, kPauseBeforeShowAnimationDuration, this,
@@ -308,10 +271,7 @@ class BackGestureContextualNudge::ContextualNudgeView
 
   // views::View:
   void Layout() override {
-    const gfx::Rect bounds = GetLocalBounds();
-    gradient_layer_delegate_->layer()->SetBounds(bounds);
-
-    gfx::Rect rect(bounds);
+    gfx::Rect rect = GetLocalBounds();
     rect.ClampToCenteredSize(gfx::Size(kBackgroundWidth, kBackgroundWidth));
     rect.set_x(-kCircleRadius);
     suggestion_view_->SetBoundsRect(rect);
@@ -320,7 +280,15 @@ class BackGestureContextualNudge::ContextualNudgeView
   // views::View:
   void OnPaint(gfx::Canvas* canvas) override {
     views::View::OnPaint(canvas);
-    canvas->DrawColor(kBackgroundColor);
+
+    // Draw the gradient background.
+    cc::PaintFlags flags;
+    flags.setAntiAlias(true);
+    flags.setStyle(cc::PaintFlags::kFill_Style);
+    flags.setShader(
+        gfx::CreateGradientShader(gfx::Point(), gfx::Point(width(), 0),
+                                  kBackgroundStartColor, kBackgroundEndColor));
+    canvas->DrawRect(gfx::Rect(size()), flags);
   }
 
   // ui::ImplicitAnimationObserver:
@@ -341,8 +309,6 @@ class BackGestureContextualNudge::ContextualNudgeView
     }
   }
 
-  std::unique_ptr<GradientLayerDelegate> gradient_layer_delegate_;
-
   // Created by ContextualNudgeView. Owned by views hierarchy.
   SuggestionView* suggestion_view_ = nullptr;