Add use counters for some of Web Speech API

SpeechGrammarList's addFromURI because it doesn't match the spec:
https://github.com/w3c/speech-api/issues/26

SpeechRecognitionEvent's interpretation and emma attributes because
they actually always return null and might be better to remove:
https://chromium.googlesource.com/chromium/src/+/7ad6ea7c2583942e86017bdd6fd5df991f6a05af/third_party/blink/renderer/modules/speech/speech_recognition_event.h#55

SpeechSynthesis#speak() to measure real SpeechSynthesis usage, like
the existing counter for SpeechRecognition#start().

Bug: 755287
Change-Id: I4f7fdcc5630887aaa051ac8ab13f72dab52c8dfb
Reviewed-on: https://chromium-review.googlesource.com/1109510Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569222}

third_party/blink/public/platform/web_feature.mojom

@@ -1943,6 +1943,10 @@ enum WebFeature {
   kMediaStreamSourceOnOfflineContext = 2477,
   kRTCDataChannelInitMaxRetransmitTime = 2478,
   kRTCPeerConnectionCreateDataChannelMaxPacketLifeTime = 2479,
+  kV8SpeechGrammarList_AddFromUri_Method = 2480,
+  kV8SpeechRecognitionEvent_Interpretation_AttributeGetter = 2481,
+  kV8SpeechRecognitionEvent_Emma_AttributeGetter = 2482,
+  kV8SpeechSynthesis_Speak_Method = 2483,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/modules/speech/speech_grammar_list.idl

@@ -31,6 +31,6 @@
 ] interface SpeechGrammarList {
     readonly attribute unsigned long length;
     getter SpeechGrammar item(unsigned long index);
-    [CallWith=ScriptState] void addFromUri(DOMString src, optional float weight);
+    [CallWith=ScriptState, Measure] void addFromUri(DOMString src, optional float weight);
     void addFromString(DOMString string, optional float weight);
 };

third_party/blink/renderer/modules/speech/speech_recognition_event.idl

@@ -32,6 +32,6 @@
     readonly attribute unsigned long resultIndex;
     readonly attribute SpeechRecognitionResultList? results;
 
-    readonly attribute Document? interpretation;
-    readonly attribute Document? emma;
+    [Measure] readonly attribute Document? interpretation;
+    [Measure] readonly attribute Document? emma;
 };

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

@@ -32,7 +32,7 @@
     readonly attribute boolean speaking;
     readonly attribute boolean paused;
 
-    void speak(SpeechSynthesisUtterance utterance);
+    [Measure] void speak(SpeechSynthesisUtterance utterance);
     void cancel();
     void pause();
     void resume();

tools/metrics/histograms/enums.xml

@@ -19028,6 +19028,11 @@ Called by update_net_error_codes.py.-->
   <int value="2478" label="RTCDataChannelInitMaxRetransmitTime"/>
   <int value="2479"
       label="RTCPeerConnectionCreateDataChannelMaxPacketLifeTime"/>
+  <int value="2480" label="V8SpeechGrammarList_AddFromUri_Method"/>
+  <int value="2481"
+      label="V8SpeechRecognitionEvent_Interpretation_AttributeGetter"/>
+  <int value="2482" label="V8SpeechRecognitionEvent_Emma_AttributeGetter"/>
+  <int value="2483" label="V8SpeechSynthesis_Speak_Method"/>
 </enum>
 
 <enum name="FeedbackSource">