[FlexibleHeader] Deprecate pre iOS 8 ToBeDeprecated APIs.

PiperOrigin-RevId: 333367145

components/FlexibleHeader/src/MDCFlexibleHeaderView.h

@@ -365,28 +365,6 @@ IB_DESIGNABLE
 
 @interface MDCFlexibleHeaderView (ToBeDeprecated)
 
-// Pre-iOS 8 Interface Orientation APIs
-
-/**
- Informs the receiver that the interface orientation is about to change.
-
- Must be called from UIViewController::willRotateToInterfaceOrientation:duration:.
- */
-- (void)interfaceOrientationWillChange;
-
-/**
- Informs the receiver that the interface orientation is in the process of changing.
-
- Must be called from UIViewController::willAnimateRotationToInterfaceOrientation:duration:.
- */
-- (void)interfaceOrientationIsChanging;
-
-/**
- Informs the receiver that the interface orientation has changed.
-
- Must be called from UIViewController::didRotateFromInterfaceOrientation:.
- */
-- (void)interfaceOrientationDidChange;
 
 /**
  When this is enabled, the flexible header will assume that minimumHeight and maximumHeight both
@@ -436,6 +414,36 @@ IB_DESIGNABLE
 
 @end
 
+@interface MDCFlexibleHeaderView (Deprecated)
+
+// Pre-iOS 8 Interface Orientation APIs
+
+/**
+ Informs the receiver that the interface orientation is about to change.
+
+ Must be called from UIViewController::willRotateToInterfaceOrientation:duration:.
+ */
+- (void)interfaceOrientationWillChange __deprecated_msg(
+    "Use viewWillTransitionToSize:withTransitionCoordinator: instead.");
+
+/**
+ Informs the receiver that the interface orientation is in the process of changing.
+
+ Must be called from UIViewController::willAnimateRotationToInterfaceOrientation:duration:.
+ */
+- (void)interfaceOrientationIsChanging __deprecated_msg(
+    "Use viewWillTransitionToSize:withTransitionCoordinator: instead.");
+
+/**
+ Informs the receiver that the interface orientation has changed.
+
+ Must be called from UIViewController::didRotateFromInterfaceOrientation:.
+ */
+- (void)interfaceOrientationDidChange __deprecated_msg(
+    "Use viewWillTransitionToSize:withTransitionCoordinator: instead.");
+
+@end
+
 // clang-format off
 @interface MDCFlexibleHeaderView ()