Add use counters for navigator.requestMediaKeySystemAccess

third_party/WebKit/public/platform/WebFeature.h

 #ifndef WebFeature_h
 #define WebFeature_h
 
 namespace blink {
 // ============ Definition for WebFeature used for UseCounter ===============
 //
 // Do not change assigned numbers of existing items: add new features
 // to the end of the list.
 //
 // A WebFeature conceptually represents some particular web-exposed API
@@ skipping 482 matching lines @@
   kSVGHrefAnimVal = 759,
   kV8CSSRuleList_Item_Method = 760,
   kV8MediaList_Item_Method = 761,
   kV8StyleSheetList_Item_Method = 762,
   kStyleSheetListAnonymousNamedGetter = 763,
   kAutocapitalizeAttribute = 764,
   kFullscreenSecureOrigin = 765,
   kFullscreenInsecureOrigin = 766,
   kDialogInSandboxedContext = 767,
   kSVGSMILAnimationInImageRegardlessOfCache = 768,
+  kEncryptedMediaSecureOrigin = 770,
   kPerformanceFrameTiming = 772,
   kV8Element_Animate_Method = 773,
   // The above items are available in M44 branch.
 
   kV8SVGSVGElement_GetElementById_Method = 778,
   kElementCreateShadowRootMultiple = 779,
   kV8MessageChannel_Constructor = 780,
   kV8MessagePort_PostMessage_Method = 781,
   kV8MessagePort_Start_Method = 782,
   kV8MessagePort_Close_Method = 783,
@@ skipping 1041 matching lines @@
   kClientHintsDeviceRAM = 2017,
   kCSSRegisterProperty = 2018,
   kRelativeOrientationSensorConstructor = 2019,
   kSmoothScrollJSInterventionActivated = 2020,
   kBudgetAPIGetCost = 2021,
   kBudgetAPIGetBudget = 2022,
   kCrossOriginMainFrameNulledNonEmptyNameAccessed = 2023,
   kDeprecatedTimingFunctionStepMiddle = 2024,
   kDocumentDomainSetWithNonDefaultPort = 2025,
   kDocumentDomainSetWithDefaultPort = 2026,
+  kEncryptedMediaIframe = 2027,

[xhwang, 2017/06/21 17:03:18]

naming nit: "Iframe" is ambiguous. It seems we already have:

AudioContextCrossOriginIframe
WebAudioAutoplayCrossOriginIframe

Should we use "EncryptedMediaCrossOriginIframe" instead?

[raymes, 2017/06/28 03:57:28]

Done.

 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.
   // Also, run update_use_counter_feature_enum.py in
   // chromium/src/tools/metrics/histograms/ to update the UMA mapping.
   kNumberOfFeatures,  // This enum value must be last.
 };
 
 }  // namespace blink
 
 #endif  // WebFeature_h