Give enums in SkImageInfo an underlying type

According to goto.google.com/chrome-includes, SkImageInfo.h is a
somewhat expensive header to include. This makes it possible to
forward-declare these enums instead.

Bug: chromium:1227131,chromium:242216
Change-Id: I4e939449a8d3dfc3fa4c43999bcaecb3249bc0c8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/431056
Commit-Queue: Nico Weber <thakis@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/include/core/SkImageInfo.h b/include/core/SkImageInfo.h
index ae31853..426c234 100644
--- a/include/core/SkImageInfo.h
+++ b/include/core/SkImageInfo.h
@@ -34,7 +34,7 @@
     value is the original RGB multiplied by alpha. Premultiplied color
     components improve performance.
 */
-enum SkAlphaType {
+enum SkAlphaType : int {
     kUnknown_SkAlphaType,                          //!< uninitialized
     kOpaque_SkAlphaType,                           //!< pixel is opaque
     kPremul_SkAlphaType,                           //!< pixel components are premultiplied by alpha
@@ -61,7 +61,7 @@
     kN32_SkColorType selects the native 32-bit ARGB format for the current configuration. This can
     lead to inconsistent results across platforms, so use with caution.
 */
-enum SkColorType {
+enum SkColorType : int {
     kUnknown_SkColorType,      //!< uninitialized
     kAlpha_8_SkColorType,      //!< pixel with alpha in 8-bit byte
     kRGB_565_SkColorType,      //!< pixel with 5 bits red, 6 bits green, 5 bits blue, in 16-bit word
@@ -145,7 +145,7 @@
     The identity colorspace exists to provide a utility mapping from Y to R, U to G and V to B.
     It can be used to visualize the YUV planes or to explicitly post process the YUV channels.
 */
-enum SkYUVColorSpace {
+enum SkYUVColorSpace : int {
     kJPEG_Full_SkYUVColorSpace,                 //!< describes full range
     kRec601_Limited_SkYUVColorSpace,            //!< describes SDTV range
     kRec709_Full_SkYUVColorSpace,               //!< describes HDTV range