Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/internal/web_view_web_client.mm

Index: ios/web_view/internal/web_view_web_client.mm
diff --git a/ios/web_view/internal/web_view_web_client.mm b/ios/web_view/internal/web_view_web_client.mm
index a9c60a05d0ff75b889784b9d4d94aec7c0e5086e..be65137eed2a1f48cfd28ea657dda5829274ba46 100644
--- a/ios/web_view/internal/web_view_web_client.mm
+++ b/ios/web_view/internal/web_view_web_client.mm
@@ -15,8 +15,7 @@
 
 namespace ios_web_view {
 
-WebViewWebClient::WebViewWebClient(const std::string& user_agent_product)
-    : user_agent_product_(user_agent_product), web_main_parts_(nullptr) {}
+WebViewWebClient::WebViewWebClient() : web_main_parts_(nullptr) {}
 
 WebViewWebClient::~WebViewWebClient() = default;
 
@@ -47,4 +46,8 @@ NSString* WebViewWebClient::GetEarlyPageScript(
       .GetScript();
 }
 
+void WebViewWebClient::SetProduct(const std::string& user_agent_product) {
+  user_agent_product_ = user_agent_product;
+}
+
 }  // namespace ios_web_view