Don't scale mask image for new tab button.

 MatchScale's 2x routine uses canvas which can't scale mask image. This routine should be gone, so I fixed it in
tab_strip, rather than fixing this routine.

 I'll flip the default value of the flag "scaling-in-image-skia-operation" so that mismatch will result in CHECK failure.

BUG=163372
TEST=none

Review URL: https://codereview.chromium.org/11684002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175394 0039d316-1c4b-4281-b951-d872f2087c98

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

@@ -426,6 +426,11 @@ gfx::ImageSkia NewTabButton::GetBackgroundImage(
       GetThemeProvider()->GetImageSkiaNamed(IDR_NEWTAB_BUTTON_MASK);
   int height = mask->height();
   int width = mask->width();
+
+  // The canvas and mask has to use the same scale factor.
+  if (!mask->HasRepresentation(scale_factor))
+    scale_factor = ui::SCALE_FACTOR_100P;
+
   gfx::Canvas canvas(gfx::Size(width, height), scale_factor, false);
 
   // For custom images the background starts at the top of the tab strip.

ui/gfx/image/image_skia_operations.cc

@@ -167,7 +167,6 @@ class MaskedImageSource : public gfx::ImageSkiaSource {
   virtual ImageSkiaRep GetImageForScale(ui::ScaleFactor scale_factor) OVERRIDE {
     ImageSkiaRep rgb_rep = rgb_.GetRepresentation(scale_factor);
     ImageSkiaRep alpha_rep = alpha_.GetRepresentation(scale_factor);
-    MatchScale(&rgb_rep, &alpha_rep);
     return ImageSkiaRep(SkBitmapOperations::CreateMaskedBitmap(
         rgb_rep.sk_bitmap(), alpha_rep.sk_bitmap()),
                         rgb_rep.scale_factor());