Deprecate speechSynthesis.speak() without user activation

See intent to deprecate:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/XpkevOngqUs

The deprecation will target M71.

Bug: 812767
Change-Id: Id4448a91047def16194a47efdacc152070dace82
Reviewed-on: https://chromium-review.googlesource.com/1157231Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580550}

third_party/blink/renderer/core/frame/deprecation.cc

@@ -579,6 +579,10 @@ DeprecationInfo GetDeprecationInfo(WebFeature feature) {
                              "https://www.chromestatus.com/feature/"
                              "6708326821789696 for more details.",
                              MilestoneString(kM70))};
+    case WebFeature::kTextToSpeech_SpeakDisallowedByAutoplay:
+      return {"TextToSpeech_DisallowedByAutoplay", kM71,
+              WillBeRemoved("speechSynthesis.speak() without user activation",
+                            kM71, "5687444770914304")};
 
     // Features that aren't deprecated don't have a deprecation message.
     default:

third_party/blink/renderer/modules/speech/speech_synthesis.cc

@@ -27,6 +27,7 @@
 
 #include "third_party/blink/renderer/core/dom/document.h"
 #include "third_party/blink/renderer/core/execution_context/execution_context.h"
+#include "third_party/blink/renderer/core/frame/deprecation.h"
 #include "third_party/blink/renderer/core/frame/use_counter.h"
 #include "third_party/blink/renderer/core/html/media/autoplay_policy.h"
 #include "third_party/blink/renderer/core/timing/dom_window_performance.h"
@@ -119,8 +120,8 @@ void SpeechSynthesis::speak(SpeechSynthesisUtterance* utterance) {
   UseCounter::CountCrossOriginIframe(
       *document, WebFeature::kTextToSpeech_SpeakCrossOrigin);
   if (!IsAllowedToStartByAutoplay()) {
-    UseCounter::Count(document,
-                      WebFeature::kTextToSpeech_SpeakDisallowedByAutoplay);
+    Deprecation::CountDeprecation(
+        document, WebFeature::kTextToSpeech_SpeakDisallowedByAutoplay);
   }
 
   utterance_queue_.push_back(utterance);