Add CWVUserContentController which enables injecting JavaScripts.

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 06f049400a0fff9f921aeeb25e8d2cbe5b367104..56aed9bfd7c5c71e84f0f0eb13f8246ffa7f82b1 100644
--- a/ios/web_view/internal/web_view_web_client.mm
+++ b/ios/web_view/internal/web_view_web_client.mm
@@ -7,6 +7,7 @@
 #include "base/strings/sys_string_conversions.h"
 #include "ios/web/public/user_agent.h"
 #include "ios/web_view/internal/web_view_browser_state.h"
+#import "ios/web_view/internal/web_view_early_page_script_provider.h"
 #import "ios/web_view/internal/web_view_web_main_parts.h"
 #import "ios/web_view/public/cwv_delegate.h"
 
@@ -42,4 +43,10 @@ std::string WebViewWebClient::GetUserAgent(web::UserAgentType type) const {
   return web::BuildUserAgentFromProduct(GetProduct());
 }
 
+NSString* WebViewWebClient::GetEarlyPageScript(
+    web::BrowserState* browser_state) const {
+  return WebViewEarlyPageScriptProvider::FromBrowserState(browser_state)
+      .GetScript();
+}
+
 }  // namespace ios_web_view