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

components/spellcheck/browser/spellcheck_platform_android.cc

Index: components/spellcheck/browser/spellcheck_platform_android.cc
diff --git a/components/spellcheck/browser/spellcheck_platform_android.cc b/components/spellcheck/browser/spellcheck_platform_android.cc
index 3d746118f94d6a769bf8ee19b6267c61b0bc6ab2..3cca6be1772c9373106fc9e0eae3aeffbffa4f19 100644
--- a/components/spellcheck/browser/spellcheck_platform_android.cc
+++ b/components/spellcheck/browser/spellcheck_platform_android.cc
@@ -6,7 +6,7 @@
 
 #include "base/callback.h"
 #include "base/command_line.h"
-#include "components/spellcheck/common/spellcheck_switches.h"
+#include "components/spellcheck/common/spellcheck_features.h"
 
 namespace spellcheck_platform {
 
@@ -18,8 +18,7 @@ std::string GetSpellCheckerLanguage() {
 }
 
 bool SpellCheckerAvailable() {
-  return base::CommandLine::ForCurrentProcess()->HasSwitch(
-      spellcheck::switches::kEnableAndroidSpellChecker);
+  return spellcheck::IsAndroidSpellCheckFeatureEnabled();
 }
 
 bool SpellCheckerProvidesPanel() {