Add AwVariationsSeedFetchService and refactory VariationsSeedFetcher

android_webview/test/BUILD.gn

Index: android_webview/test/BUILD.gn
diff --git a/android_webview/test/BUILD.gn b/android_webview/test/BUILD.gn
index 0a0b40e063c109ad248420896537eb3c190dc872..d4403a0377b5f3ae0b100e747f3a2fa7f3da5690 100644
--- a/android_webview/test/BUILD.gn
+++ b/android_webview/test/BUILD.gn
@@ -115,6 +115,7 @@ instrumentation_test_apk("webview_instrumentation_test_apk") {
     "//components/policy/android:policy_java",
     "//components/policy/android:policy_java_test_support",
     "//components/safe_browsing_db/android:safe_browsing_java",
+    "//components/variations/android:variations_java",
     "//components/web_contents_delegate_android:web_contents_delegate_android_java",
     "//content/public/android:content_java",
     "//content/public/test/android:content_java_test_support",
@@ -164,6 +165,7 @@ instrumentation_test_apk("webview_instrumentation_test_apk") {
     "../javatests/src/org/chromium/android_webview/test/AwStrictModeTest.java",
     "../javatests/src/org/chromium/android_webview/test/AwTestBase.java",
     "../javatests/src/org/chromium/android_webview/test/AwWebContentsObserverTest.java",
+    "../javatests/src/org/chromium/android_webview/test/AwVariationsSeedFetchServiceTest.java",
     "../javatests/src/org/chromium/android_webview/test/AwZoomTest.java",
     "../javatests/src/org/chromium/android_webview/test/CleanupReferenceTest.java",
     "../javatests/src/org/chromium/android_webview/test/ClearHistoryTest.java",