Enable unified garbage collections part two

This flag overrides the default Blink value for content layer.

Sheriffs: This is a dry-run of the feature and will be reverted after
cycling through the waterfall and performance bots.

Tbr: jochen@chromium.org, lfg@chromium.org
Bug: 843903
Change-Id: Ie362301e4874198eb775346d051bf8267837aaf8
Reviewed-on: https://chromium-review.googlesource.com/c/1320970
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606446}

chrome/browser/apps/guest_view/web_view_browsertest.cc

@@ -3539,7 +3539,11 @@ IN_PROC_BROWSER_TEST_F(WebViewTest, BasicPostMessage) {
 }
 
 // Tests that webviews do get garbage collected.
-IN_PROC_BROWSER_TEST_F(WebViewTest, Shim_TestGarbageCollect) {
+// This test is disabled because it relies on garbage collections triggered from
+// window.gc() to run precisely. This is not the case with unified heap where
+// they need to conservatively scan the stack, potentially keeping objects
+// alive. https://crbug.com/843903
+IN_PROC_BROWSER_TEST_F(WebViewTest, DISABLED_Shim_TestGarbageCollect) {
   TestHelper("testGarbageCollect", "web_view/shim", NO_TEST_SERVER);
   GetGuestViewManager()->WaitForSingleViewGarbageCollected();
 }

content/public/common/content_features.cc

@@ -64,7 +64,7 @@ const base::Feature kBlinkHeapIncrementalMarking{
 
 // Enable unified garbage collection in Blink.
 const base::Feature kBlinkHeapUnifiedGarbageCollection{
-    "BlinkHeapUnifiedGarbageCollection", base::FEATURE_DISABLED_BY_DEFAULT};
+    "BlinkHeapUnifiedGarbageCollection", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable bloated renderer detection.
 const base::Feature kBloatedRendererDetection{

third_party/WebKit/LayoutTests/fast/dom/StyleSheet/gc-rule-children-wrappers-expected.txt

@@ -17,7 +17,7 @@ PASS document.styleSheets[0].cssRules[3].media.foo is 'bar'
 PASS document.styleSheets[0].cssRules[4].type is CSSRule.KEYFRAMES_RULE
 PASS document.styleSheets[0].cssRules[4].cssRules.foo is 'bar'
 PASS document.styleSheets[0].cssRules[4].cssRules[0].type is CSSRule.KEYFRAME_RULE
-FAIL document.styleSheets[0].cssRules[4].cssRules[0].style.foo should be bar (of type string). Was undefined (of type undefined).
+PASS document.styleSheets[0].cssRules[4].cssRules[0].style.foo is 'bar'
 PASS document.styleSheets[0].cssRules[5].type is CSSRule.PAGE_RULE
 PASS document.styleSheets[0].cssRules[5].style.foo is 'bar'
 PASS successfullyParsed is true

third_party/WebKit/LayoutTests/fast/dom/gc-9-expected.txt

@@ -64,10 +64,10 @@ PASS: document.body.childNodes.myCustomProperty should be 1 and is.
 PASS: document.body.dataset.myCustomProperty should be 1 and is.
 PASS: document.body.classList.myCustomProperty should be 1 and is.
 PASS: document.getElementsByTagName('link')[0].relList.myCustomProperty should be 1 and is.
-FAIL: document.getElementsByTagName('link')[0].sizes.myCustomProperty should be 1 but instead is undefined.
-FAIL: document.getElementsByTagName('output')[0].htmlFor.myCustomProperty should be 1 but instead is undefined.
+PASS: document.getElementsByTagName('link')[0].sizes.myCustomProperty should be 1 and is.
+PASS: document.getElementsByTagName('output')[0].htmlFor.myCustomProperty should be 1 and is.
 PASS: document.getElementsByTagName('output')[0].labels.myCustomProperty should be 1 and is.
-FAIL: document.getElementsByTagName('iframe')[0].sandbox.myCustomProperty should be 1 but instead is undefined.
+PASS: document.getElementsByTagName('iframe')[0].sandbox.myCustomProperty should be 1 and is.
 PASS: document.all.myCustomProperty should be 1 and is.
 PASS: document.images.myCustomProperty should be 1 and is.
 PASS: document.embeds.myCustomProperty should be 1 and is.
@@ -83,7 +83,7 @@ PASS: document.getElementsByTagName('table')[0].tBodies.myCustomProperty should
 PASS: document.getElementsByTagName('table')[0].tBodies[0].rows.myCustomProperty should be 1 and is.
 PASS: document.body.children.myCustomProperty should be 1 and is.
 PASS: document.getElementsByTagName('map')[0].areas.myCustomProperty should be 1 and is.
-FAIL: document.body.style.myCustomProperty should be 1 but instead is undefined.
+PASS: document.body.style.myCustomProperty should be 1 and is.
 PASS: document.styleSheets.myCustomProperty should be 1 and is.
 PASS: document.styleSheets[0].myCustomProperty should be 1 and is.
 PASS: document.styleSheets[0].cssRules.myCustomProperty should be 1 and is.

third_party/WebKit/LayoutTests/fast/xpath/xpath-iterator-result-should-mark-its-nodeset-expected.txt

 Test for bug 34231: Nodes in XPathResult should keep JS wrappers alive.
 For this test to PASS you should see 2 PASS below.
 
-undefined
-undefined
+PASS
+PASS
 

third_party/WebKit/LayoutTests/fast/xpath/xpath-other-nodeset-result-should-mark-its-nodeset-expected.txt

 Test for bug 34231: Nodes in XPath result snapshots should keep JS wrappers alive.
 For this test to PASS you should see 2 PASS below.
 
-undefined
-undefined
+PASS
+PASS
 

third_party/WebKit/LayoutTests/fast/xpath/xpath-snapshot-result-should-mark-its-nodeset-expected.txt

 Test for bug 34231: Nodes in XPath result snapshots should keep JS wrappers alive.
 For this test to PASS you should see 2 PASS below.
 
-undefined
-undefined
+PASS
+PASS