[blink/bindings] Enable ParkableStringsToDisk by default.

From the dev/beta/stable experiments, this reduces memory by multiple
MiB per renderer @95th percentile, with larger savings on popular
websites (7MiB on Facebook at the median on desktop, for instance).

Enable it by default.

Bug: 1029320
Change-Id: Iaa355d50f80617b2a8eb763984761a5cc3d5aae3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410041Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807418}

third_party/blink/common/features.cc

@@ -722,7 +722,7 @@ const base::Feature kCompressParkableStrings{"CompressParkableStrings",
 // Whether ParkableStrings can be written out to disk.
 // Depends on compression above.
 const base::Feature kParkableStringsToDisk{"ParkableStringsToDisk",
-                                           base::FEATURE_DISABLED_BY_DEFAULT};
+                                           base::FEATURE_ENABLED_BY_DEFAULT};
 
 bool IsParkableStringsToDiskEnabled() {
   return base::FeatureList::IsEnabled(kParkableStringsToDisk) &&

third_party/blink/renderer/platform/bindings/parkable_string_test.cc

@@ -864,6 +864,13 @@ TEST_F(ParkableStringTest, CompressionDisabled) {
   EXPECT_FALSE(parkable.Impl()->may_be_parked());
 }
 
+TEST_F(ParkableStringTest, CompressionDisabledDisablesDisk) {
+  base::test::ScopedFeatureList features;
+  features.InitAndDisableFeature(features::kCompressParkableStrings);
+
+  EXPECT_FALSE(features::IsParkableStringsToDiskEnabled());
+}
+
 TEST_F(ParkableStringTest, Aging) {
   ParkableString parkable(MakeLargeString().ReleaseImpl());
   EXPECT_EQ(ParkableStringImpl::Age::kYoung,