Change LowerJavaScriptPriorityWhenForceDeferred to Disabled by default

LowerJavaScriptPriorityWhenForceDeferred feature is currently enabled
by default. This CL changes it to disabled by default.
This change enables us to experiment with this feature
(whether it actually helps in the performance or not).

Change-Id: I39ec2b4f55550eee870be4d4d26283b92c960952
Bug: 978490
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1824419Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Auto-Submit: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707465}

chrome/browser/previews/defer_all_script_priority_browsertest.cc

@@ -36,6 +36,7 @@
 #include "content/public/test/browser_test_utils.h"
 #include "net/test/embedded_test_server/http_request.h"
 #include "net/test/embedded_test_server/http_response.h"
+#include "third_party/blink/public/common/features.h"
 
 namespace {
 
@@ -80,6 +81,7 @@ class DeferAllScriptPriorityBrowserTest
       scoped_feature_list_.InitWithFeatures(
           {previews::features::kPreviews,
            previews::features::kDeferAllScriptPreviews,
+           blink::features::kLowerJavaScriptPriorityWhenForceDeferred,
            optimization_guide::features::kOptimizationHints,
            data_reduction_proxy::features::
                kDataReductionProxyEnabledWithNetworkService},
@@ -87,6 +89,7 @@ class DeferAllScriptPriorityBrowserTest
     } else {
       scoped_feature_list_.InitWithFeatures(
           {previews::features::kPreviews,
+           blink::features::kLowerJavaScriptPriorityWhenForceDeferred,
            optimization_guide::features::kOptimizationHints,
            data_reduction_proxy::features::
                kDataReductionProxyEnabledWithNetworkService},

testing/variations/fieldtrial_testing_config.json

@@ -3262,6 +3262,21 @@
             ]
         }
     ],
+    "LowerJavaScriptPriorityWhenForceDeferred": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Control_20190905",
+                    "disable_features": [
+                        "LowerJavaScriptPriorityWhenForceDeferred"
+                    ]
+                }
+            ]
+        }
+    ],
     "LsdPermissionPrompt": [
         {
             "platforms": [

third_party/blink/common/features.cc

@@ -397,7 +397,7 @@ const base::Feature kIgnoreCrossOriginWindowWhenNamedAccessOnWindow{
 // are force deferred by the intervention.
 const base::Feature kLowerJavaScriptPriorityWhenForceDeferred{
     "LowerJavaScriptPriorityWhenForceDeferred",
-    base::FEATURE_ENABLED_BY_DEFAULT};
+    base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kHtmlImportsRequestInitiatorLock{
     "HtmlImportsRequestInitiatorLock", base::FEATURE_ENABLED_BY_DEFAULT};