MacViews: Implement scrollbar theming.

ui/native_theme/native_theme_mac.mm

Index: ui/native_theme/native_theme_mac.mm
diff --git a/ui/native_theme/native_theme_mac.mm b/ui/native_theme/native_theme_mac.mm
index 2477af8ea0b3b20754a2e138685c892134c67f06..e33749ba11079364840ffa0fa7f55c4b1dfe1e3b 100644
--- a/ui/native_theme/native_theme_mac.mm
+++ b/ui/native_theme/native_theme_mac.mm
@@ -12,10 +12,18 @@
 #include "base/mac/sdk_forward_declarations.h"
 #include "ui/native_theme/common_theme.h"
 #import "skia/ext/skia_utils_mac.h"
+#include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/skia_util.h"
 
 namespace {
 
+const SkColor kScrollerTrackColor = SkColorSetRGB(0xF8, 0xF8, 0xF8);

[tapted, 2014/08/11 01:00:58]

Can we make this a horizontal 3-stage gradient, to match a little closer?

[Andre, 2014/08/12 21:42:38]

Done.

+const SkColor kScrollerTrackBorderColor = SkColorSetRGB(0xE4, 0xE4, 0xE4);
+const SkColor kScrollerThumbColor = SkColorSetRGB(0xC3, 0xC3, 0xC3);

[tapted, 2014/08/11 01:00:58]

These should have an alpha component, so the track gradient shows through. it
looks like there's also a PaintStateTransition(..) function that will allow the
fade-in effect to be done -- can we do this by refactoring some code out of
native_theme_aura for some code re-use?

[Andre, 2014/08/12 21:42:37]

Added alpha component, although the effect is very subtle.
PaintStateTransition(..) appears to be unused and never called.
I think we should tackle fade effects in a separate CL since it will involve
modifying views code.

+const SkColor kScrollerThumbHoverColor = SkColorSetRGB(0x7E, 0x7E, 0x7E);
+const int kScrollerTrackBorderWidth = 1;
+const int kScrollerThumbInset = 3;
+
 // Values calculated by reading pixels and solving simultaneous equations
 // derived from "A over B" alpha compositing. Steps: Sample the semi-transparent
 // pixel over two backgrounds; P1, P2 over backgrounds B1, B2. Use the color
@@ -216,7 +224,61 @@ void NativeThemeMac::PaintMenuItemBackground(
   }
 }
 
+void NativeThemeMac::PaintScrollbarTrack(

[tapted, 2014/08/11 01:00:58]

(nit: move up in the .mm file too)

[Andre, 2014/08/12 21:42:37]

Done.

+    SkCanvas* canvas,
+    Part part,
+    State state,
+    const ScrollbarTrackExtraParams& extra_params,
+    const gfx::Rect& rect) const {
+  SkPaint paint;
+  paint.setColor(track_color_);

[tapted, 2014/08/11 01:00:58]

probably something like paint.setShader(SkGradientShader::CreateLinear(..)); 

[Andre, 2014/08/12 21:42:38]

Done.

+  SkIRect track_rect;
+  track_rect.set(rect.x(), rect.y(), rect.right(), rect.bottom());
+  canvas->drawIRect(track_rect, paint);
+
+  // Draw line border next to content area.
+  paint.setColor(kScrollerTrackBorderColor);
+  if (part == kScrollbarVerticalTrack) {
+    canvas->drawRectCoords(track_rect.left(),
+                           track_rect.top(),
+                           track_rect.left() + kScrollerTrackBorderWidth,
+                           track_rect.bottom(),
+                           paint);
+  } else {
+    canvas->drawRectCoords(track_rect.left(),
+                           track_rect.top(),
+                           track_rect.right(),
+                           track_rect.top() + kScrollerTrackBorderWidth,
+                           paint);
+  }
+}
+
+void NativeThemeMac::PaintScrollbarThumb(SkCanvas* canvas,
+                                         Part part,
+                                         State state,
+                                         const gfx::Rect& rect) const {
+  gfx::Rect thumb_rect(rect);
+  if (part == kScrollbarVerticalThumb)

[tapted, 2014/08/11 01:00:58]

Maybe a switch statement here, with NOTREACHED(). (i.e. follow
NativeThemeWin::PaintScrollbarThumb(..) more closely). There are also "gripper"
parts, (which common theme ignores).

[Andre, 2014/08/12 21:42:38]

Done.

+    thumb_rect.Inset(kScrollerTrackBorderWidth, 0, 0, 0);
+  else
+    thumb_rect.Inset(0, kScrollerTrackBorderWidth, 0, 0);
+
+  thumb_rect.Inset(kScrollerThumbInset, kScrollerThumbInset);
+
+  SkPaint paint;
+  paint.setColor(state == kHovered ? thumb_active_color_
+                                   : thumb_inactive_color_);
+  SkRect skrect;
+  skrect.set(
+      thumb_rect.x(), thumb_rect.y(), thumb_rect.right(), thumb_rect.bottom());
+  const SkScalar radius = std::min(skrect.width(), skrect.height());
+  canvas->drawRoundRect(skrect, radius, radius, paint);
+}
+
 NativeThemeMac::NativeThemeMac() {
+  set_scrollbar_button_length(0);

[tapted, 2014/08/11 01:00:58]

Perhaps also override PaintArrowButton to be a no-op? there's some complex
drawing code there it would be nice to avoid.

[Andre, 2014/08/12 21:42:38]

I've added a scrollbar_button_length_ check in NativeThemeBase::Paint() instead.
WDYT?

[tapted, 2014/08/13 01:13:29]

lg

+  SetScrollbarColors(
+      kScrollerThumbColor, kScrollerThumbHoverColor, kScrollerTrackColor);
 }
 
 NativeThemeMac::~NativeThemeMac() {