Media Capabilities: mark encoding API experimental

Encoding API was mistakenly promoted stable earlier. This CL fixes this
and introduces a new MediaCapabilitiesEncodingInfo runtime enabled
feature marked as experimental.

Bug: 824708
Change-Id: I8f06982471ee544919fe427f782b8d8ccf21f7b5
Reviewed-on: https://chromium-review.googlesource.com/970463
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545036}

third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt

@@ -3631,7 +3631,6 @@ interface MediaCapabilities
     attribute @@toStringTag
     method constructor
     method decodingInfo
-    method encodingInfo
 interface MediaCapabilitiesInfo
     attribute @@toStringTag
     getter powerEfficient

third_party/WebKit/Source/modules/media_capabilities/MediaCapabilities.idl

@@ -4,11 +4,9 @@
 
 // https://wicg.github.io/media-capabilities/#mediacapabilities
 
-[
-    Exposed=Window,
-    OriginTrialEnabled=MediaCapabilities
-] interface MediaCapabilities {
-    [CallWith=ScriptState, Measure] Promise<MediaCapabilitiesInfo> decodingInfo(MediaDecodingConfiguration configuration);
-    [CallWith=ScriptState, Measure] Promise<MediaCapabilitiesInfo> encodingInfo(
+[Exposed=Window]
+interface MediaCapabilities {
+    [CallWith=ScriptState, Measure, OriginTrialEnabled=MediaCapabilities] Promise<MediaCapabilitiesInfo> decodingInfo(MediaDecodingConfiguration configuration);
+    [CallWith=ScriptState, Measure, RuntimeEnabled=MediaCapabilitiesEncodingInfo] Promise<MediaCapabilitiesInfo> encodingInfo(
         MediaEncodingConfiguration configuration);
 };

third_party/WebKit/Source/platform/runtime_enabled_features.json5

@@ -623,6 +623,10 @@
       origin_trial_feature_name: "MediaCapabilities",
       status: "stable",
     },
+    {
+      name: "MediaCapabilitiesEncodingInfo",
+      status: "experimental",
+    },
     {
       name: "MediaCapture",
     },