Let CRIWVWebView inherit UIView instead of NSObject.

ios/web_view/internal/criwv_web_view_internal.h

Index: ios/web_view/internal/criwv_web_view_internal.h
diff --git a/ios/web_view/internal/criwv_web_view_impl.h b/ios/web_view/internal/criwv_web_view_internal.h
similarity index 67%
rename from ios/web_view/internal/criwv_web_view_impl.h
rename to ios/web_view/internal/criwv_web_view_internal.h
index fbd9170e9ab082c8b473e93215212f296da232d6..6fe403d4bd3dbab3a2a2ad237be2b5a3ed4a146e 100644
--- a/ios/web_view/internal/criwv_web_view_impl.h
+++ b/ios/web_view/internal/criwv_web_view_internal.h
@@ -11,12 +11,12 @@ namespace ios_web_view {
 class CRIWVBrowserState;
 }
 
-@interface CRIWVWebViewImpl : NSObject<CRIWVWebView>
+@interface CRIWVWebView ()
 
-- (instancetype)init NS_UNAVAILABLE;
-
-- (instancetype)initWithBrowserState:
-    (ios_web_view::CRIWVBrowserState*)browserState NS_DESIGNATED_INITIALIZER;
+// |browserState| cannot be nil.
+- (instancetype)initWithFrame:(CGRect)frame
+                 browserState:(ios_web_view::CRIWVBrowserState*)browserState
+    NS_DESIGNATED_INITIALIZER;
 
 @end