Enable YieldBetweenContentScriptRuns by default

Bug: 705400
Change-Id: Iffc701df6997a0341839cf5b294694ffd5dc20d8
Reviewed-on: https://chromium-review.googlesource.com/887999
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532769}

extensions/common/extension_features.cc

@@ -16,8 +16,9 @@ const base::Feature kNewExtensionUpdaterService{
     "NewExtensionUpdaterService", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables splitting content script injections into multiple tasks.
+// TODO(ksakamoto): Remove this feature flag in M67.
 const base::Feature kYieldBetweenContentScriptRuns{
-    "YieldBetweenContentScriptRuns", base::FEATURE_DISABLED_BY_DEFAULT};
+    "YieldBetweenContentScriptRuns", base::FEATURE_ENABLED_BY_DEFAULT};
 
 }  // namespace features
 }  // namespace extensions