[Android] Allow setting recently visited search engines as default search engine

chrome/browser/search_engines/template_url_service_android.h

Index: chrome/browser/search_engines/template_url_service_android.h
diff --git a/chrome/browser/search_engines/template_url_service_android.h b/chrome/browser/search_engines/template_url_service_android.h
index af5f38c08a212727731e298448ae5df747711b74..acf02babbc6761f0ae44fa3fbdca5357d2d10cd1 100644
--- a/chrome/browser/search_engines/template_url_service_android.h
+++ b/chrome/browser/search_engines/template_url_service_android.h
@@ -27,7 +27,12 @@ class TemplateUrlServiceAndroid : public TemplateURLServiceObserver {
   void SetUserSelectedDefaultSearchProvider(
       JNIEnv* env,
       const base::android::JavaParamRef<jobject>& obj,
-      jint selected_index);
+      const base::android::JavaParamRef<jstring>& jkeyword);
+  // Update template_urls and return the index of default search provider in the
+  // list. Note that this function will also reorder the list so that if any
+  // custom search engine is set as default, it will be placed before the rest
+  // of
+  // custom ones and after all the prepopulated ones.
   jint GetDefaultSearchProvider(
       JNIEnv* env,
       const base::android::JavaParamRef<jobject>& obj);
@@ -71,15 +76,13 @@ class TemplateUrlServiceAndroid : public TemplateURLServiceObserver {
   base::android::ScopedJavaLocalRef<jstring> GetSearchEngineUrlFromTemplateUrl(
       JNIEnv* env,
       const base::android::JavaParamRef<jobject>& obj,
-      jint index);
+      const base::android::JavaParamRef<jstring>& jkeyword);
 
   static bool Register(JNIEnv* env);
 
  private:
   ~TemplateUrlServiceAndroid() override;
 
-  bool IsPrepopulatedTemplate(TemplateURL* url);
-
   void OnTemplateURLServiceLoaded();
 
   // TemplateUrlServiceObserver:
@@ -92,6 +95,8 @@ class TemplateUrlServiceAndroid : public TemplateURLServiceObserver {
 
   std::unique_ptr<TemplateURLService::Subscription> template_url_subscription_;
 
+  std::vector<TemplateURL*> template_urls_;
+
   DISALLOW_COPY_AND_ASSIGN(TemplateUrlServiceAndroid);
 };