Add a feature flag for optimizing workers for performance

This fixes a mistake in crrev.com/747632 where the flag was added as
a runtime-enabled feature that is not visible to Finch. The flag now is
moved to blink/public/common/features.h

Bug: 1049132
Change-Id: I2d13e6cb97fd57535861379ae5fc80dba9dc252d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2102547Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750207}

third_party/blink/common/features.cc

@@ -159,6 +159,11 @@ const base::Feature kRTCUnifiedPlanByDefault{"RTCUnifiedPlanByDefault",
 const base::Feature kRTCOfferExtmapAllowMixed{
     "RTCOfferExtmapAllowMixed", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Prevents workers from sending IsolateInBackgroundNotification to V8
+// and thus instructs V8 to favor performance over memory on workers.
+const base::Feature kV8OptimizeWorkersForPerformance{
+    "V8OptimizeWorkersForPerformance", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enables negotiation of experimental multiplex codec in SDP.
 const base::Feature kWebRtcMultiplexCodec{"WebRTC-MultiplexCodec",
                                           base::FEATURE_DISABLED_BY_DEFAULT};

third_party/blink/public/common/features.h

@@ -45,6 +45,7 @@ BLINK_COMMON_EXPORT extern const base::Feature kRawClipboard;
 BLINK_COMMON_EXPORT extern const base::Feature kRTCGetDisplayMedia;
 BLINK_COMMON_EXPORT extern const base::Feature kRTCUnifiedPlanByDefault;
 BLINK_COMMON_EXPORT extern const base::Feature kRTCOfferExtmapAllowMixed;
+BLINK_COMMON_EXPORT extern const base::Feature kV8OptimizeWorkersForPerformance;
 BLINK_COMMON_EXPORT extern const base::Feature kWebRtcMultiplexCodec;
 BLINK_COMMON_EXPORT extern const base::Feature kWebRtcHideLocalIpsWithMdns;
 

third_party/blink/renderer/core/workers/worker_backing_thread.cc

@@ -7,6 +7,7 @@
 #include <memory>
 
 #include "base/location.h"
+#include "third_party/blink/public/common/features.h"
 #include "third_party/blink/public/platform/platform.h"
 #include "third_party/blink/public/web/blink.h"
 #include "third_party/blink/renderer/bindings/core/v8/v8_binding_for_core.h"
@@ -83,7 +84,8 @@ void WorkerBackingThread::InitializeOnBackingThread(
   V8PerIsolateData::From(isolate_)->SetThreadDebugger(
       std::make_unique<WorkerThreadDebugger>(isolate_));
 
-  if (!RuntimeEnabledFeatures::V8OptimizeWorkersForPerformanceEnabled()) {
+  if (!base::FeatureList::IsEnabled(
+          features::kV8OptimizeWorkersForPerformance)) {
     // Optimize for memory usage instead of latency for the worker isolate.
     // Service Workers that have the fetch event handler run with the Isolate
     // in foreground notification regardless of this configuration.

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1739,10 +1739,6 @@
     {
       name: "V8IdleTasks",
     },
-    {
-      name: "V8OptimizeWorkersForPerformance",
-      status: "experimental",
-    },
     {
       // Whether a video element should automatically play fullscreen unless
       // 'playsinline' is set.