Desktop PWAs: Add a blink feature flag for web app protocol handling.

Adds and binds a blink feature flag to control web app protocol handling
features.

A previous CL has already added the runtime_enabled_features.json5 entry:
https://chromium-review.googlesource.com/c/chromium/src/+/2211200

Explainer: https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/master/URLProtocolHandler/explainer.md
Design doc: https://docs.google.com/document/d/1NHlWLjAPZ-dyxcz3AoTWibeerDeHW7Vqrx6FmhB0XmE/edit

Bug: 1019239
Change-Id: I5ef9ac247f180f5edd4f0734422de5826c0d3465
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2506395Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Samuel Tang <samtan@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#822672}

content/child/runtime_features.cc

@@ -320,6 +320,8 @@ void SetRuntimeFeaturesFromChromiumFeatures() {
      blink::features::kCompositingOptimizations},
     {wf::EnableConversionMeasurementInfraSupport,
      features::kConversionMeasurement},
+    {wf::EnableParseUrlProtocolHandler,
+     blink::features::kWebAppEnableProtocolHandlers},
   };
   for (const auto& mapping : blinkFeatureToBaseFeatureMapping) {
     SetRuntimeFeatureFromChromiumFeature(

third_party/blink/common/features.cc

@@ -783,6 +783,13 @@ const base::Feature kLogUnexpectedIPCPostedToBackForwardCachedDocuments{
 const base::Feature kWebAppEnableUrlHandlers{"WebAppEnableUrlHandlers",
                                              base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables Protocol handling feature in web apps. Controls parsing of
+// "protocol_handlers" field in web app manifests. See explainer for more
+// information:
+// https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/URLProtocolHandler/explainer.md
+const base::Feature kWebAppEnableProtocolHandlers{
+    "WebAppEnableProtocolHandlers", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // When enabled NV12 frames on a GPU will be forwarded to libvpx encoders
 // without conversion to I420.
 const base::Feature kWebRtcLibvpxEncodeNV12{"WebRtcLibvpxEncodeNV12",

third_party/blink/public/common/features.h

@@ -317,6 +317,7 @@ BLINK_COMMON_EXPORT extern const base::Feature
     kLogUnexpectedIPCPostedToBackForwardCachedDocuments;
 
 BLINK_COMMON_EXPORT extern const base::Feature kWebAppEnableUrlHandlers;
+BLINK_COMMON_EXPORT extern const base::Feature kWebAppEnableProtocolHandlers;
 BLINK_COMMON_EXPORT extern const base::Feature kWebRtcLibvpxEncodeNV12;
 }  // namespace features
 }  // namespace blink

third_party/blink/public/platform/web_runtime_features.h

@@ -258,6 +258,8 @@ class WebRuntimeFeatures {
 
   BLINK_PLATFORM_EXPORT static void EnableCompositingOptimizations(bool);
 
+  BLINK_PLATFORM_EXPORT static void EnableParseUrlProtocolHandler(bool);
+
  private:
   WebRuntimeFeatures();
 };

third_party/blink/renderer/platform/exported/web_runtime_features.cc

@@ -739,4 +739,8 @@ void WebRuntimeFeatures::EnableConversionMeasurementInfraSupport(bool enable) {
   RuntimeEnabledFeatures::SetConversionMeasurementInfraSupportEnabled(enable);
 }
 
+void WebRuntimeFeatures::EnableParseUrlProtocolHandler(bool enable) {
+  RuntimeEnabledFeatures::SetParseUrlProtocolHandlerEnabled(enable);
+}
+
 }  // namespace blink