Make cc/paint have concrete types

cc/layers/painted_overlay_scrollbar_layer.cc

Index: cc/layers/painted_overlay_scrollbar_layer.cc
diff --git a/cc/layers/painted_overlay_scrollbar_layer.cc b/cc/layers/painted_overlay_scrollbar_layer.cc
index 4f64e9e3d7dce2176ff0bfe13351fab150df6373..88485046eb05dcf398f9a5753aa6ad6f3a3ff07e 100644
--- a/cc/layers/painted_overlay_scrollbar_layer.cc
+++ b/cc/layers/painted_overlay_scrollbar_layer.cc
@@ -140,16 +140,16 @@ bool PaintedOverlayScrollbarLayer::PaintThumbIfNeeded() {
 
   SkBitmap skbitmap;
   skbitmap.allocN32Pixels(paint_rect.width(), paint_rect.height());
-  SkCanvas skcanvas(skbitmap);
+  PaintCanvas canvas(skbitmap);
 
   SkRect content_skrect = RectToSkRect(paint_rect);
-  SkPaint paint;
-  paint.setAntiAlias(false);
-  paint.setBlendMode(SkBlendMode::kClear);
-  skcanvas.drawRect(content_skrect, paint);
-  skcanvas.clipRect(content_skrect);
+  PaintFlags flags;
+  flags.setAntiAlias(false);
+  flags.setBlendMode(SkBlendMode::kClear);
+  canvas.drawRect(content_skrect, flags);
+  canvas.clipRect(content_skrect);
 
-  scrollbar_->PaintPart(&skcanvas, THUMB, paint_rect);
+  scrollbar_->PaintPart(&canvas, THUMB, paint_rect);
   // Make sure that the pixels are no longer mutable to unavoid unnecessary
   // allocation and copying.
   skbitmap.setImmutable();