[COEP] Enable on all platforms (e.g. add Android WebView)

There are no real reasons for COEP not to be enforced on Android
WebView.

See also:

[PSA-COEP-expanded-to-webview]:
https://groups.google.com/a/chromium.org/g/blink-dev/c/Wc_uYYkcviw

[Updated chrome-status entry]:
https://chromestatus.com/features/5642721685405696

[original-intent-to-ship-coep]:
https://groups.google.com/a/chromium.org/g/blink-dev/c/XBKAGb2_7uA/m/ajpc6_9zAAAJ

[crossOriginIsolated spec to be updated]:
https://github.com/whatwg/html/issues/6060

Bug: 1140432
Change-Id: I9a7c44671846f20bd0ac2a06b181ed584ad606eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485507Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Domenic Denicola <domenic@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820311}

android_webview/lib/aw_main_delegate.cc

@@ -240,10 +240,9 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
     // De-jelly is never supported on WebView.
     features.EnableIfNotSet(::features::kDisableDeJelly);
 
-    // COOP/COEP is not supported on WebView. See:
+    // COOP is not supported on WebView yet. See:
     // https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/XBKAGb2_7uAi.
     features.DisableIfNotSet(network::features::kCrossOriginOpenerPolicy);
-    features.DisableIfNotSet(network::features::kCrossOriginEmbedderPolicy);
 
     features.DisableIfNotSet(::features::kInstalledApp);
 

services/network/public/cpp/features.cc

@@ -70,6 +70,7 @@ const base::Feature kProactivelyThrottleLowPriorityRequests{
 
 // Enables Cross-Origin Opener Policy (COOP).
 // https://gist.github.com/annevk/6f2dd8c79c77123f39797f6bdac43f3e
+// https://html.spec.whatwg.org/#cross-origin-opener-policy
 // Currently this feature is enabled for all platforms except WebView.
 const base::Feature kCrossOriginOpenerPolicy{"CrossOriginOpenerPolicy",
                                              base::FEATURE_ENABLED_BY_DEFAULT};
@@ -96,8 +97,10 @@ const base::Feature kCrossOriginOpenerPolicyByDefault{
     "CrossOriginOpenerPolicyByDefault", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables Cross-Origin Embedder Policy (COEP).
-// https://github.com/mikewest/corpp
-// Currently this feature is enabled for all platforms except WebView.
+// https://html.spec.whatwg.org/#coep
+// Currently this feature is enabled for all platforms (including webview).
+// TODO(https://crbug.com/1140432): Remove this flag after M88 Stable + 1 week =
+// 2021-02-01.
 const base::Feature kCrossOriginEmbedderPolicy{
     "CrossOriginEmbedderPolicy", base::FEATURE_ENABLED_BY_DEFAULT};