Enable the PageLifecycle feature by default

This feature is already enabled on Stable, see https://cs.chromium.org/chromium/src/third_party/blink/renderer/platform/runtime_enabled_features.json5?l=901&rcl=ba0d48f8b3e768e554f6b30d7ab04e3f0e907e61

Change-Id: I070350276f861f717bcb1cf51e45cb7dc8963c1b
Reviewed-on: https://chromium-review.googlesource.com/c/1327445Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606744}

content/public/common/content_features.cc

@@ -294,7 +294,7 @@ const base::Feature kOverscrollHistoryNavigation{
 
 // Blink PageLifecycle feature. See https://crbug.com/775194
 const base::Feature kPageLifecycle{"PageLifecycle",
-                                   base::FEATURE_DISABLED_BY_DEFAULT};
+                                   base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Whether document level event listeners should default 'passive' to true.
 const base::Feature kPassiveDocumentEventListeners{

testing/variations/fieldtrial_testing_config.json

@@ -4650,7 +4650,6 @@
                         "mainThreadTaskLoadLowThreshold": "25"
                     },
                     "enable_features": [
-                        "PageLifecycle",
                         "ProactiveTabFreezeAndDiscard",
                         "stop-non-timers-in-background"
                     ]