win: Don't VIEWS_EXPORT ImagePainter.

ImagePainter is in an unnamed namespace, exporting it makes no sense.

Fixes
..\..\ui\views\painter.cc(187,15) :  error(clang): 'views::(anonymous namespace)::ImagePainter::ImagePainter' must have external linkage when declared 'dllexport'
ImagePainter::ImagePainter(const int image_ids[])
              ^
on the clang/win components bot.

BUG=82385
R=msw@chromium.org

Review URL: https://codereview.chromium.org/496123003

Cr-Commit-Position: refs/heads/master@{#291950}

ui/views/painter.cc

@@ -163,7 +163,7 @@ void GradientPainter::Paint(gfx::Canvas* canvas, const gfx::Size& size) {
 // ImagePainter ---------------------------------------------------------------
 
 // ImagePainter stores and paints nine images as a scalable grid.
-class VIEWS_EXPORT ImagePainter : public Painter {
+class ImagePainter : public Painter {
  public:
   // Constructs an ImagePainter with the specified image resource ids.
   // See CreateImageGridPainter()'s comment regarding image ID count and order.