Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/internal/web_view_web_client.h

Index: ios/web_view/internal/web_view_web_client.h
diff --git a/ios/web_view/internal/web_view_web_client.h b/ios/web_view/internal/web_view_web_client.h
index 22b657dfcaea20e9a3fbead7d5055d9538e75b42..3669813b6214859104421dd68f9926e39e0b9d54 100644
--- a/ios/web_view/internal/web_view_web_client.h
+++ b/ios/web_view/internal/web_view_web_client.h
@@ -17,7 +17,7 @@ class WebViewWebMainParts;
 // WebView implementation of WebClient.
 class WebViewWebClient : public web::WebClient {
  public:
-  explicit WebViewWebClient(const std::string& user_agent_product);
+  WebViewWebClient();
   ~WebViewWebClient() override;
 
   // WebClient implementation.
@@ -26,6 +26,9 @@ class WebViewWebClient : public web::WebClient {
   std::string GetUserAgent(web::UserAgentType type) const override;
   NSString* GetEarlyPageScript(web::BrowserState* browser_state) const override;
 
+  // Setter to modify the User Agent product.
+  void SetProduct(const std::string& user_agent_product);
+
   // Normal browser state associated with the receiver.
   WebViewBrowserState* browser_state() const;
   // Off the record browser state  associated with the receiver.