Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/public/cwv_web_view.h

Index: ios/web_view/public/cwv_web_view.h
diff --git a/ios/web_view/public/cwv_web_view.h b/ios/web_view/public/cwv_web_view.h
index 1989c9e775fe69e0ea21a8873917656713125ff6..32d57e2e50df3dc7fab5747db2fae5b1c2cafa3a 100644
--- a/ios/web_view/public/cwv_web_view.h
+++ b/ios/web_view/public/cwv_web_view.h
@@ -54,6 +54,18 @@ CWV_EXPORT
 // is reset to 0.0.
 @property(nonatomic, readonly) double estimatedProgress;
 
+// The User Agent product string used to build the full User Agent.
++ (NSString*)userAgentProduct;
+
+// Customizes the User Agent string by inserting |product|. It should be of the
+// format "product/1.0".
+// NOTE: It is recommended to set |product| before initializing any web views.
+//
+// Setting |product| is only guaranteed to affect web views which have not yet
+// been initialized. However, exisiting web views could also be affected
+// depending upon their internal state.
++ (void)setUserAgentProduct:(NSString*)product;
+
 // |configuration| must not be null
 - (instancetype)initWithFrame:(CGRect)frame
                 configuration:(CWVWebViewConfiguration*)configuration