When autoplay of muted videos is disabled, record the reason why.

third_party/WebKit/Source/core/html/AutoplayUmaHelper.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef AutoplayUmaHelper_h
 #define AutoplayUmaHelper_h
 
 #include "core/events/EventListener.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 // These values are used for histograms. Do not reorder.
 enum class AutoplaySource {
     // Autoplay comes from HTMLMediaElement `autoplay` attribute.
     Attribute = 0,
     // Autoplay comes from `play()` method.
     Method = 1,
     // This enum value must be last.
     NumberOfSources = 2,
 };
 
 // These values are used for histograms. Do not reorder.
 enum class AutoplayUnmuteActionStatus {
     Failure = 0,
     Success = 1,
     NumberOfStatus = 2,
 };
 
+// These values are used for histograms. Do not reorder.
+enum AutoplayBlockedReason {
+    AutoplayBlockedReasonDataSaver = 0,
+    AutoplayBlockedReasonSetting = 1,
+    AutoplayBlockedReasonDataSaverAndSetting = 2,
+    // Keey at the end.
+    AutoplayBlockedReasonMax = 3
+};
+
 class Document;
 class ElementVisibilityObserver;
 class HTMLMediaElement;
 
 class AutoplayUmaHelper final : public EventListener {
 public:
     static AutoplayUmaHelper* create(HTMLMediaElement*);
 
     ~AutoplayUmaHelper();
 
@@ skipping 21 matching lines @@
     AutoplaySource m_source;
     // The media element this UMA helper is attached to. |m_element| owns |this|.
     WeakMember<HTMLMediaElement> m_element;
     // The observer is used to observe whether a muted video autoplaying by play() method become visible at some point.
     Member<ElementVisibilityObserver> m_videoMutedPlayMethodVisibilityObserver;
 };
 
 } // namespace blink
 
 #endif // AutoplayUmaHelper_h