Disable Shadow DOM v0 and Custom Elements v0

```yaml
IN CASE OF PROBLEMS: If this CL causes your site/app to break, you are
using deprecated features that have now been removed. Please see [2] to
enroll in the Deprecation Extension program to give yourself more time.
```

With this CL, two of the three Web Components v0 APIs are disabled by
default. The third, HTML Imports, will be disabled (soon) by a separate CL.

These features were deprecated in August, 2018, in [1]. The original
removal timeline called for a deadline of M73. Due to high use counters
for the features, this deadline was extended to M80, which is now here.
For those sites that need additional time, there is a "deprecation
extension" (sometimes called a "reverse origin trial") that can be used
to extend this removal for specific sites through M87. For more
information on that, see [2]. For overall context on this removal,
including motivation and ways to test/upgrade, see [3].

With this CL, these features will still be enabled for testing across
all test suites. Once this CL has had a chance to land and stabilize,
subsequent CLs will disable the features for all tests by default, and
enable a virtual test suite to continue testing specific code with WCv0
features enabled, to ensure the features continue to function through
the end of the deprecation extension period.

[1] https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/h-JwMiPUnuU/sl79aLoLBQAJ
[2] https://developers.chrome.com/origintrials/#/view_trial/2431943798780067841
[3] https://developers.google.com/web/updates/2019/07/web-components-time-to-upgrade

Bug: 911943
Change-Id: I939e1ead03a3196e63f0f9c192f916c87ab16562
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1850795Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Darin Fisher <darin@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708031}

third_party/blink/renderer/core/html/html_link_element.cc

@@ -70,7 +70,8 @@ void HTMLLinkElement::ParseAttribute(
   const AtomicString& value = params.new_value;
   if (name == kRelAttr) {
     rel_attribute_ = LinkRelAttribute(value);
-    if (rel_attribute_.IsImport()) {
+    if (rel_attribute_.IsImport() &&
+        RuntimeEnabledFeatures::HTMLImportsEnabledByRuntimeFlag()) {
       Deprecation::CountDeprecation(&GetDocument(), WebFeature::kHTMLImports);
     }
     rel_list_->DidUpdateAttributeValue(params.old_value, value);

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -502,12 +502,12 @@
       name: "CustomElementDefaultStyle",
       status: "experimental",
     },
-    // Introduced this flag as stable so web developers can test their sites
-    // without native Custom Elements v0 support.
+    // TODO(937746): Web Components v0 is disabled by default, and will be
+    // removed after M87.
     {
       name: "CustomElementsV0",
       origin_trial_feature_name: "WebComponentsV0",
-      status: "stable",
+      status: "test",
     },
     {
       name: "CustomStatePseudoClass",
@@ -763,7 +763,8 @@
       origin_trial_feature_name: "HrefTranslate",
       status: "experimental",
     },
-    // https://crbug.com/766694 for testing disabling the feature.
+    // TODO(911943): HTML Imports is temporarily being left enabled after
+    // the planned removal milestone of M80.
     {
       name: "HTMLImports",
       origin_trial_feature_name: "WebComponentsV0",
@@ -773,10 +774,11 @@
     {
       name: "HTMLImportsOnlyChrome",
     },
-    // https://crbug.com/523952 for testing disabling the feature.
+    // TODO(937746): Web Components v0 is disabled by default, and will be
+    // removed after M87.
     {
       name: "HTMLImportsStyleApplication",
-      status: "stable",
+      status: "test",
     },
     {
       name: "IDBObserver",
@@ -1499,12 +1501,12 @@
       name: "SetRootScroller",
       status: "experimental",
     },
-    // Introduced this flag as stable so web developers can test their sites
-    // without native Shadow DOM v0 support
+    // TODO(937746): Web Components v0 is disabled by default, and will be
+    // removed after M87.
     {
       name: "ShadowDOMV0",
       origin_trial_feature_name: "WebComponentsV0",
-      status: "stable",
+      status: "test",
     },
     {
       name: "ShadowPiercingDescendantCombinator",

third_party/blink/web_tests/virtual/origin-trials-runtimeflags-disabled/http/tests/origin_trials/webexposed/webcomponentsv0-usecounter-htmlimports-expected.txt

+This is a testharness.js-based test.
+FAIL Comfirm HTMLImportsOnReverseOriginTrials counter assert_true: expected true got false
+Harness: the test ran to completion.
+

third_party/blink/web_tests/virtual/stable/webexposed/custom-elements-expected.txt

+Tests basic web-exposure of Custom Elements
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+Document.prototype.hasOwnProperty("registerElement")
+false
+
+
+typeof Document.prototype.registerElement
+undefined
+
+
+document.createElement("x-a") instanceof HTMLUnknownElement
+false
+
+
+document.querySelector(":unresolved")
+FAIL document.querySelector(":unresolved") threw exception SyntaxError: Failed to execute 'querySelector' on 'Document': ':unresolved' is not a valid selector.
+undefined
+
+
+span.getAttribute("is")
+
+
+PASS window.customElements.define("a-a", A, {extends: "b"}) did not throw exception.
+PASS successfullyParsed is true
+
+TEST COMPLETE
+

third_party/blink/web_tests/virtual/stable/webexposed/element-instance-property-listing-expected.txt

@@ -55,7 +55,6 @@ namespace http://www.w3.org/1999/xhtml
     property computedStyleMap
     property contains
     property contentEditable
-    property createShadowRoot
     property dataset
     property dir
     property dispatchEvent
@@ -72,7 +71,6 @@ namespace http://www.w3.org/1999/xhtml
     property getAttributeNodeNS
     property getBoundingClientRect
     property getClientRects
-    property getDestinationInsertionPoints
     property getElementsByClassName
     property getElementsByTagName
     property getElementsByTagNameNS
@@ -1167,7 +1165,6 @@ namespace http://www.w3.org/2000/svg
     property compareDocumentPosition
     property computedStyleMap
     property contains
-    property createShadowRoot
     property dataset
     property dispatchEvent
     property elementTiming
@@ -1181,7 +1178,6 @@ namespace http://www.w3.org/2000/svg
     property getAttributeNodeNS
     property getBoundingClientRect
     property getClientRects
-    property getDestinationInsertionPoints
     property getElementsByClassName
     property getElementsByTagName
     property getElementsByTagNameNS

third_party/blink/web_tests/virtual/stable/webexposed/global-interface-listing-expected.txt

@@ -1447,7 +1447,6 @@ interface Document : Node
     method queryCommandValue
     method querySelector
     method querySelectorAll
-    method registerElement
     method releaseEvents
     method webkitCancelFullScreen
     method webkitExitFullscreen
@@ -1656,7 +1655,6 @@ interface Element : Node
     method closest
     method computedStyleMap
     method constructor
-    method createShadowRoot
     method getAttribute
     method getAttributeNS
     method getAttributeNames
@@ -1664,7 +1662,6 @@ interface Element : Node
     method getAttributeNodeNS
     method getBoundingClientRect
     method getClientRects
-    method getDestinationInsertionPoints
     method getElementsByClassName
     method getElementsByTagName
     method getElementsByTagNameNS
@@ -6872,7 +6869,6 @@ interface Text : CharacterData
     getter assignedSlot
     getter wholeText
     method constructor
-    method getDestinationInsertionPoints
     method splitText
 interface TextDecoder
     attribute @@toStringTag

tools/perf/page_sets/data/system_health_desktop.json

@@ -27,9 +27,6 @@
             "mac": "system_health_desktop_040.wprgo",
             "win": "system_health_desktop_047.wprgo"
         },
-        "browse:media:youtube:2018": {
-            "DEFAULT": "system_health_desktop_6b6bdda708.wprgo"
-        },
         "browse:media:youtubetv:2019": {
             "DEFAULT": "system_health_desktop_e53598d1f4.wprgo"
         },
@@ -375,4 +372,4 @@
     },
     "description": "Describes the Web Page Replay archives for a story set. Don't edit by hand! Use record_wpr for updating.",
     "platform_specific": true
-}
+}
\ No newline at end of file

tools/perf/page_sets/system_health/browsing_stories.py

@@ -257,7 +257,7 @@ class RedditMobileStory2019(_ArticleBrowsingStory):
     for i in xrange(self.ITEMS_TO_VISIT + 1):
       # Skip the ad disguised as an article.
       if i == 1:
-           continue
+        continue
       self._NavigateToItem(action_runner, i)
       self._ReadNextArticle(action_runner)
       self._NavigateBack(action_runner)
@@ -604,23 +604,6 @@ class YouTubeMobileStory(_MediaBrowsingStory):
           story_tags.HEALTH_CHECK, story_tags.YEAR_2016]
 
 
-class YouTubeDesktopStory2018(_MediaBrowsingStory):
-  """Load a typical YouTube video then navigate to a next few videos. Stop and
-  watch each video for a few seconds.
-  """
-  NAME = 'browse:media:youtube:2018'
-  URL = 'https://www.youtube.com/watch?v=QGfhS1hfTWw&autoplay=0'
-  ITEM_SELECTOR = 'ytd-compact-video-renderer.ytd-watch-next-secondary-results-renderer a'
-  SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
-  IS_SINGLE_PAGE_APP = True
-  # A longer view time allows videos to load and play.
-  ITEM_VIEW_TIME_IN_SECONDS = 5
-  ITEMS_TO_VISIT = 8
-  ITEM_SELECTOR_INDEX = 3
-  PLATFORM_SPECIFIC = True
-  TAGS = [story_tags.JAVASCRIPT_HEAVY, story_tags.YEAR_2018]
-
-
 class YouTubeTVDesktopStory2019(_MediaBrowsingStory):
   """Load a typical YouTube TV video then navigate to a next few videos. Stop
   and watch each video for a few seconds.