Start removing the double-negative !ASSERT_DISABLED

Source/platform/image-decoders/ImageFrame.h

Index: Source/platform/image-decoders/ImageFrame.h
diff --git a/Source/platform/image-decoders/ImageFrame.h b/Source/platform/image-decoders/ImageFrame.h
index 9ae4c8fa4e0db369f74b5efc0072ce42f5137175..e44f07a15844bb558128fd7b070e6a4fc0e2b53f 100644
--- a/Source/platform/image-decoders/ImageFrame.h
+++ b/Source/platform/image-decoders/ImageFrame.h
@@ -128,7 +128,7 @@ public:
         ASSERT(m_requiredPreviousFrameIndexValid);
         return m_requiredPreviousFrameIndex;
     }
-#if !ASSERT_DISABLED
+#if ASSERT_ENABLED
     bool requiredPreviousFrameIndexValid() const { return m_requiredPreviousFrameIndexValid; }
 #endif
     void setHasAlpha(bool alpha);
@@ -147,7 +147,7 @@ public:
     void setRequiredPreviousFrameIndex(size_t previousFrameIndex)
     {
         m_requiredPreviousFrameIndex = previousFrameIndex;
-#if !ASSERT_DISABLED
+#if ASSERT_ENABLED
         m_requiredPreviousFrameIndexValid = true;
 #endif
     }
@@ -234,7 +234,7 @@ private:
     // This is used by ImageDecoder::clearCacheExceptFrame(), and will never
     // be read for image formats that do not have multiple frames.
     size_t m_requiredPreviousFrameIndex;
-#if !ASSERT_DISABLED
+#if ASSERT_ENABLED
     bool m_requiredPreviousFrameIndexValid;
 #endif
 };