skia/ext: Add SK_API to a function used from a test

skia/ext/bitmap_platform_device_mac.h

Index: skia/ext/bitmap_platform_device_mac.h
diff --git a/skia/ext/bitmap_platform_device_mac.h b/skia/ext/bitmap_platform_device_mac.h
index f57a36eb51b988223be455b7a704bd867aa7fb04..822790c8ea835a7c3a11baf71f24efb53366594f 100644
--- a/skia/ext/bitmap_platform_device_mac.h
+++ b/skia/ext/bitmap_platform_device_mac.h
@@ -26,7 +26,7 @@ namespace skia {
 // For us, that other bitmap will become invalid as soon as the device becomes
 // invalid, which may lead to subtle bugs. Therefore, DO NOT ASSIGN THE
 // DEVICE'S PIXEL DATA TO ANOTHER BITMAP, make sure you copy instead.
-class BitmapPlatformDevice : public PlatformDevice, public SkDevice {
+class SK_API BitmapPlatformDevice : public PlatformDevice, public SkDevice {
  public:
   // |context| may be NULL.
   static BitmapPlatformDevice* Create(CGContextRef context,