Enable NonValidatingReloadOnRefreshContentV2 feature by default

Now the feature is approved to roll out into Stable channel,
let me flip the feature flag to be enabled by default.

This is a required process to launch the feature through the field study,
and should be done before the feature is rolled out to 100%.

BUG=591245

Review-Url: https://codereview.chromium.org/2296603002
Cr-Commit-Position: refs/heads/master@{#415569}

content/public/common/content_features.cc

@@ -76,7 +76,7 @@ const base::Feature kNonValidatingReloadOnNormalReload{
 // See https://crbug.com/591245
 const base::Feature kNonValidatingReloadOnRefreshContent{
     "NonValidatingReloadOnRefreshContentV2",
-    base::FEATURE_DISABLED_BY_DEFAULT};
+    base::FEATURE_ENABLED_BY_DEFAULT};
 
 // An experiment to optimize resource loading IPC for small resources.
 // http://crbug.com/580928