PrefetchScheduler: Add feature flag for WebView

Bug: 406403063
Change-Id: I0fe0f8a3efd7fbfbc8e0a7a6a9170c990abad38a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6440782
Auto-Submit: Ken Okada <kenoss@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Ken Okada <kenoss@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1444543}

android_webview/java/src/org/chromium/android_webview/common/ProductionSupportedFlagList.java

@@ -1082,6 +1082,7 @@ public final class ProductionSupportedFlagList {
         Flag.baseFeature(
                 MediaFeatures.MULTI_BUFFER_NEVER_DEFER,
                 "Controls behavior of network deferrals during media src=file playbacks."),
+        Flag.baseFeature("PrefetchScheduler"),
         // Add new commandline switches and features above. The final entry should have a
         // trailing comma for cleaner diffs.
     };