Revert of Replace requirePageReconstruction with setCustomUserAgent

ios/web/web_state/ui/crw_web_controller.h

Index: ios/web/web_state/ui/crw_web_controller.h
diff --git a/ios/web/web_state/ui/crw_web_controller.h b/ios/web/web_state/ui/crw_web_controller.h
index 0b22741099f2c768db206dd405efb8dcaf29fef9..b7706278b98e7d772674bceb418ae1ce6dd2c5d0 100644
--- a/ios/web/web_state/ui/crw_web_controller.h
+++ b/ios/web/web_state/ui/crw_web_controller.h
@@ -191,6 +191,14 @@
 // Dismisses the soft keyboard.
 - (void)dismissKeyboard;
 
+// Requires that the next load rebuild the UIWebView. This is expensive, and
+// should be used only in the case where something has changed that UIWebView
+// only checks on creation, such that the whole object needs to be rebuilt.
+// TODO(stuartmorgan): Merge this and reinitializeWebViewAndReload:. They are
+// currently subtly different in terms of implementation, but are for
+// fundamentally the same purpose.
+- (void)requirePageReconstruction;
+
 - (void)reinitializeWebViewAndReload:(BOOL)reload;
 
 // Requires that the next display reload the page, using a placeholder while