Do not use borders when setting padding on tab close button.

This is a start at eliminating redundant layouts and memory allocations
during layout in the tabstrip. Instead of a border, we use
kInternalPaddingKey with a pre-allocated gfx::Insets. This is the same
approach used by ToolbarButton and will also help if tabs are switched
to using a layout manager.

Ultimately, we want to eliminate both allocation of border objets as
well as all layout invalidations during layout.

Bug: 1121681
Change-Id: Icf7ac6c93eda5ccf80639ab95b2e0c705c1c5d45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375741
Commit-Queue: Dana Fried <dfried@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801572}

chrome/browser/ui/views/tabs/tab.cc

@@ -348,8 +348,7 @@ void Tab::Layout() {
     const int left = std::min(after_title_padding, close_x);
     const int bottom = height() - close_button_size - top;
     const int right = std::max(0, width() - (close_x + close_button_size));
-    close_button_->SetBorder(
-        views::CreateEmptyBorder(top, left, bottom, right));
+    close_button_->SetButtonPadding(gfx::Insets(top, left, bottom, right));
     close_button_->SetBoundsRect(
         {gfx::Point(close_x - left, 0), close_button_->GetPreferredSize()});
   }

chrome/browser/ui/views/tabs/tab_close_button.cc

@@ -27,6 +27,7 @@
 #include "ui/views/controls/highlight_path_generator.h"
 #include "ui/views/layout/layout_provider.h"
 #include "ui/views/rect_based_targeting_utils.h"
+#include "ui/views/view_class_properties.h"
 
 #if defined(USE_AURA)
 #include "ui/aura/env.h"
@@ -73,6 +74,10 @@ TabCloseButton::TabCloseButton(views::ButtonListener* listener,
       std::make_unique<views::CircleHighlightPathGenerator>(gfx::Insets());
   ring_highlight_path->set_use_contents_bounds(true);
   focus_ring()->SetPathGenerator(std::move(ring_highlight_path));
+
+  // Always have a value on this property so we can modify it directly without
+  // a heap allocation.
+  SetProperty(views::kInternalPaddingKey, gfx::Insets());
 }
 
 TabCloseButton::~TabCloseButton() {}
@@ -90,6 +95,10 @@ void TabCloseButton::SetIconColors(SkColor foreground_color,
       color_utils::GetColorWithMaxContrast(background_color));
 }
 
+void TabCloseButton::SetButtonPadding(const gfx::Insets& padding) {
+  *GetProperty(views::kInternalPaddingKey) = padding;
+}
+
 const char* TabCloseButton::GetClassName() const {
   return "TabCloseButton";
 }
@@ -130,12 +139,13 @@ void TabCloseButton::OnGestureEvent(ui::GestureEvent* event) {
   event->SetHandled();
 }
 
+gfx::Insets TabCloseButton::GetInsets() const {
+  return ImageButton::GetInsets() + *GetProperty(views::kInternalPaddingKey);
+}
+
 gfx::Size TabCloseButton::CalculatePreferredSize() const {
-  int width = GetGlyphSize();
-  gfx::Size size(width, width);
-  gfx::Insets insets = GetInsets();
-  size.Enlarge(insets.width(), insets.height());
-  return size;
+  const int glyph_size = GetGlyphSize();
+  return gfx::Size(glyph_size, glyph_size) + GetInsets().size();
 }
 
 void TabCloseButton::PaintButtonContents(gfx::Canvas* canvas) {

chrome/browser/ui/views/tabs/tab_close_button.h

@@ -39,6 +39,13 @@ class TabCloseButton : public views::ImageButton,
   // theme changes.
   void SetIconColors(SkColor foreground_color, SkColor background_color);
 
+  // Sets the desired padding around the icon. Only the icon is a target for
+  // mouse clicks, but the entire button is a target for touch events, since the
+  // button itself is small. Note that this is cheaper than, for example,
+  // installing a new EmptyBorder every time we want to change the padding
+  // around the icon.
+  void SetButtonPadding(const gfx::Insets& padding);
+
   // views::ImageButton:
   const char* GetClassName() const override;
   View* GetTooltipHandlerForPoint(const gfx::Point& point) override;
@@ -46,6 +53,7 @@ class TabCloseButton : public views::ImageButton,
   void OnMouseReleased(const ui::MouseEvent& event) override;
   void OnMouseMoved(const ui::MouseEvent& event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
+  gfx::Insets GetInsets() const override;
 
  protected:
   // views::ImageButton: