Ship TextEncoderStream and TextDecoderStream

Mark them as "stable" in runtime_enabled_features.json5. The runtime
flag will be removed once M71 has shipped.

Intent to Ship thread:
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/jx2joIL5SbU/pGuwgvi7EAAJ

BUG=845427

Change-Id: I1fa93383958fbd3de64936375937730c27f8d1da
Reviewed-on: https://chromium-review.googlesource.com/1212431Reviewed-by: Yoav Weiss <yoav@yoav.ws>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590298}

third_party/WebKit/LayoutTests/virtual/stable/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt

@@ -1043,11 +1043,25 @@ interface TextDecoder
     getter ignoreBOM
     method constructor
     method decode
+interface TextDecoderStream
+    attribute @@toStringTag
+    getter encoding
+    getter fatal
+    getter ignoreBOM
+    getter readable
+    getter writable
+    method constructor
 interface TextEncoder
     attribute @@toStringTag
     getter encoding
     method constructor
     method encode
+interface TextEncoderStream
+    attribute @@toStringTag
+    getter encoding
+    getter readable
+    getter writable
+    method constructor
 interface TransformStream
     getter readable
     getter writable

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

@@ -980,11 +980,25 @@ Starting worker: resources/global-interface-listing-worker.js
 [Worker]     getter ignoreBOM
 [Worker]     method constructor
 [Worker]     method decode
+[Worker] interface TextDecoderStream
+[Worker]     attribute @@toStringTag
+[Worker]     getter encoding
+[Worker]     getter fatal
+[Worker]     getter ignoreBOM
+[Worker]     getter readable
+[Worker]     getter writable
+[Worker]     method constructor
 [Worker] interface TextEncoder
 [Worker]     attribute @@toStringTag
 [Worker]     getter encoding
 [Worker]     method constructor
 [Worker]     method encode
+[Worker] interface TextEncoderStream
+[Worker]     attribute @@toStringTag
+[Worker]     getter encoding
+[Worker]     getter readable
+[Worker]     getter writable
+[Worker]     method constructor
 [Worker] interface TransformStream
 [Worker]     getter readable
 [Worker]     getter writable

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

@@ -6483,11 +6483,25 @@ interface TextDecoder
     getter ignoreBOM
     method constructor
     method decode
+interface TextDecoderStream
+    attribute @@toStringTag
+    getter encoding
+    getter fatal
+    getter ignoreBOM
+    getter readable
+    getter writable
+    method constructor
 interface TextEncoder
     attribute @@toStringTag
     getter encoding
     method constructor
     method encode
+interface TextEncoderStream
+    attribute @@toStringTag
+    getter encoding
+    getter readable
+    getter writable
+    method constructor
 interface TextEvent : UIEvent
     attribute @@toStringTag
     getter data

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

@@ -980,11 +980,25 @@ Starting worker: resources/global-interface-listing-worker.js
 [Worker]     getter ignoreBOM
 [Worker]     method constructor
 [Worker]     method decode
+[Worker] interface TextDecoderStream
+[Worker]     attribute @@toStringTag
+[Worker]     getter encoding
+[Worker]     getter fatal
+[Worker]     getter ignoreBOM
+[Worker]     getter readable
+[Worker]     getter writable
+[Worker]     method constructor
 [Worker] interface TextEncoder
 [Worker]     attribute @@toStringTag
 [Worker]     getter encoding
 [Worker]     method constructor
 [Worker]     method encode
+[Worker] interface TextEncoderStream
+[Worker]     attribute @@toStringTag
+[Worker]     getter encoding
+[Worker]     getter readable
+[Worker]     getter writable
+[Worker]     method constructor
 [Worker] interface TransformStream
 [Worker]     getter readable
 [Worker]     getter writable

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -392,7 +392,7 @@
     },
     {
       name: "EncodingStreams",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "EncryptedMediaEncryptionSchemeQuery",