[Android] Add AndroidSpellChecker feature to allow for gradual rollout using finch.

android_webview/browser/aw_content_browser_client.cc

Index: android_webview/browser/aw_content_browser_client.cc
diff --git a/android_webview/browser/aw_content_browser_client.cc b/android_webview/browser/aw_content_browser_client.cc
index 97fe96de612e21deaef58b4de317dc97ef31b6ce..dbb8c83f694bc111308bfad9dce1430e14d6b4bb 100644
--- a/android_webview/browser/aw_content_browser_client.cc
+++ b/android_webview/browser/aw_content_browser_client.cc
@@ -225,10 +225,7 @@ void AwContentBrowserClient::RenderProcessWillLaunch(
   host->AddFilter(new AwPrintingMessageFilter(host->GetID()));
 
 #if defined(ENABLE_SPELLCHECK)
-  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-      spellcheck::switches::kEnableAndroidSpellChecker)) {
-    host->AddFilter(new SpellCheckMessageFilterPlatform(host->GetID()));
-  }
+  host->AddFilter(new SpellCheckMessageFilterPlatform(host->GetID()));
 #endif
 }