skhdr::AdaptiveGlobalToneMap: Add SK_API to sub-structures

Also remove operator== because the body doesn't exist.

Bug: 468928417
Change-Id: Ie05548f5047e90e7169c9e224c0df9d7251c662f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1140556
Commit-Queue: Christopher Cameron <ccameron@google.com>
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Christopher Cameron <ccameron@google.com>

include/private/SkHdrMetadata.h

diff --git a/include/private/SkHdrMetadata.h b/include/private/SkHdrMetadata.h
index b0eb530..8d4ae94 100644
--- a/include/private/SkHdrMetadata.h
+++ b/include/private/SkHdrMetadata.h
@@ -133,7 +133,7 @@
  */
 struct SK_API AdaptiveGlobalToneMap {
     // A GainCurve metadata group.
-    struct GainCurve {
+    struct SK_API GainCurve {
         // Structure holding one entry of the GainCurveControlPointX, GainCurveControlPointY, and
         // GainCurveControlPointM metadata items.
         struct ControlPoint {
@@ -149,7 +149,7 @@
     };
 
     // A ComponentMix metadata group.
-    struct ComponentMixingFunction {
+    struct SK_API ComponentMixingFunction {
         // The ComponentMixRed/Green/Blue/Max/Min/Component metadata items.
         float fRed = 0.f;
         float fGreen = 0.f;
@@ -160,7 +160,7 @@
     };
 
     // A ColorGainFunction metadata group.
-    struct ColorGainFunction {
+    struct SK_API ColorGainFunction {
         // The ComponentMix metadata group.
         ComponentMixingFunction fComponentMixing;
 
@@ -169,7 +169,7 @@
     };
 
     // Structure holding the metadata items and groups for an alternate image.
-    struct AlternateImage {
+    struct SK_API AlternateImage {
         // The AlternateHdrHeadroom metadata item.
         float fHdrHeadroom = 0.f;
 
@@ -178,7 +178,7 @@
     };
 
     // HeadroomAdaptiveToneMap metadata group.
-    struct HeadroomAdaptiveToneMap {
+    struct SK_API HeadroomAdaptiveToneMap {
         HeadroomAdaptiveToneMap();
 
         // The BaselineHdrHeadroom metadata item.
@@ -216,11 +216,6 @@
      * Return a human-readable description.
      */
     SkString toString() const;
-
-    bool operator==(const AdaptiveGlobalToneMap& other) const;
-    bool operator!=(const AdaptiveGlobalToneMap& other) const {
-        return !(*this == other);
-    }
 };
 
 /**