Add skia::RefPtr class to wrap ref counted classes from Skia.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index b09cc01adae39af445dc9620bf65e76b9fcce054..3449e2e69682d4a131e25b218ad4f004b57db617 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -674,10 +674,9 @@ void RenderWidget::PaintRect(const gfx::Rect& rect,
   // If there is a custom background, tile it.
   if (!background_.empty()) {
     SkPaint paint;
-    SkShader* shader = SkShader::CreateBitmapShader(background_,
-                                                    SkShader::kRepeat_TileMode,
-                                                    SkShader::kRepeat_TileMode);
-    paint.setShader(shader)->unref();
+    skia::RefPtr<SkShader> shader = SkShader::CreateBitmapShader(
+        background_, SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode);
+    paint.setShader(shader.get());
 
     // Use kSrc_Mode to handle background_ transparency properly.
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);