Add AwVariationsSeedFetchService and refactory VariationsSeedFetcher

android_webview/BUILD.gn

Index: android_webview/BUILD.gn
diff --git a/android_webview/BUILD.gn b/android_webview/BUILD.gn
index c5b5d16e3b1fb5f4a2aa894e55f4f6d4b3ff0cfc..71a7cd8a492ab2c47df0b60c1ea5d5e4b753f8e9 100644
--- a/android_webview/BUILD.gn
+++ b/android_webview/BUILD.gn
@@ -809,6 +809,7 @@ android_library("android_webview_java") {
     "java/src/org/chromium/android_webview/AwTokenBindingManager.java",
     "java/src/org/chromium/android_webview/AwViewMethods.java",
     "java/src/org/chromium/android_webview/AwViewAndroidDelegate.java",
+    "java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java",
     "java/src/org/chromium/android_webview/AwWebContentsDelegate.java",
     "java/src/org/chromium/android_webview/AwWebContentsDelegateAdapter.java",
     "java/src/org/chromium/android_webview/AwWebContentsObserver.java",
@@ -849,6 +850,7 @@ android_library("android_webview_java") {
     "//components/navigation_interception/android:navigation_interception_java",
     "//components/policy/android:policy_java",
     "//components/safe_browsing_db/android:safe_browsing_java",
+    "//components/variations/android:variations_java",
     "//components/web_contents_delegate_android:web_contents_delegate_android_java",
     "//components/web_restrictions:client_java",
     "//content/public/android:content_java",