Let CRIWVWebView inherit UIView instead of NSObject.

ios/web_view/public/criwv_web_view.h

Index: ios/web_view/public/criwv_web_view.h
diff --git a/ios/web_view/public/criwv_web_view.h b/ios/web_view/public/criwv_web_view.h
index 5d2aeb40c8d23a2b966d557e8457885401ee639b..d15a72e892c91e3fc433272f13b0ae117493c30b 100644
--- a/ios/web_view/public/criwv_web_view.h
+++ b/ios/web_view/public/criwv_web_view.h
@@ -10,7 +10,7 @@
 
 // Primary objective-c interface for web/.  Just like a WKWebView, but better.

[Eugene But (OOO till 7-30), 2017/02/02 20:54:32]

Do you want to update this comment? This is not an interface for web/ anymore.
Also "better" part is very subjective :). I think the comments should explain
that CRIWVWebView is responsible for rendering web content and in addition to
WKWebView allows Translate, Find In Page and Customizable Context Menus, <maybe
something else?>

[Hiroshi Ichikawa, 2017/02/03 02:14:57]

Done.

 // Concrete instances can be created through CRIWV.
-@protocol CRIWVWebView<NSObject>
+@interface CRIWVWebView : UIView
 
 // The view used to display web content.
 @property(nonatomic, readonly) UIView* view;
@@ -35,6 +35,9 @@
 // undefined if the web view is not currently loading.
 @property(nonatomic, readonly) CGFloat loadProgress;
 
+- (instancetype)initWithFrame:(CGRect)frame NS_UNAVAILABLE;
+- (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
+
 // Navigates backwards or forwards by one page.  Does nothing if the
 // corresponding |canGoBack| or |canGoForward| method returns NO.
 - (void)goBack;