image-skia: Remove implicit conversion to SkBitmap on linux and chromeos.

ui/gfx/image/image_skia_unittest.cc

Index: ui/gfx/image/image_skia_unittest.cc
diff --git a/ui/gfx/image/image_skia_unittest.cc b/ui/gfx/image/image_skia_unittest.cc
index 789fbe24359add6f09a1fdef1c56821d049492b9..20d9d452fa23edfa6ee1a9c31c370748da6df4e2 100644
--- a/ui/gfx/image/image_skia_unittest.cc
+++ b/ui/gfx/image/image_skia_unittest.cc
@@ -188,6 +188,7 @@ TEST(ImageSkiaTest, GetBitmapFromEmpty) {
   EXPECT_TRUE(bitmap->empty());
 }
 
+#if defined(OS_MACOSX) || defined(OS_WIN)
 TEST(ImageSkiaTest, OperatorBitmapFromSource) {
   ImageSkia image_skia(new DynamicSource(Size(100, 200)), Size(100, 200));
   // ImageSkia should use the source to create the bitmap.
@@ -195,6 +196,7 @@ TEST(ImageSkiaTest, OperatorBitmapFromSource) {
   ASSERT_NE(static_cast<SkBitmap*>(NULL), &bitmap);
   EXPECT_FALSE(bitmap.isNull());
 }
+#endif
 
 TEST(ImageSkiaTest, BackedBySameObjectAs) {
   // Null images should all be backed by the same object (NULL).