feat: Trace mediaCapabilities.decodingInfo

This allows us to properly log EME access that originated through
MediaCapabilities.

Change-Id: I3edb81e9d8c5f4f5c622f33a7c133a740cc30aef

eme-trace-config.js

@@ -191,6 +191,13 @@ const options = {
 
 // These will be shimmed in place.
 TraceAnything.traceMember(navigator, 'requestMediaKeySystemAccess', options);
+TraceAnything.traceMember(
+    navigator.mediaCapabilities, 'decodingInfo', combineOptions(options, {
+      // The result from decodingInfo is a plain object.  We need to dive into
+      // this field in particular to find MediaKeySystemAccess instances to
+      // trace.
+      exploreResultFields: ['keySystemAccess'],
+    }));
 
 // These constructors are not used directly, but this registers them to the
 // tracing system so that instances we find later will be shimmed.

spec/eme-trace-tests.js

@@ -75,7 +75,6 @@ describe('EME tracing', () => {
     beforeEach(async () => {
       mksa = await navigator.requestMediaKeySystemAccess(
           keySystem, minimalConfigs);
-      emeLogger.calls.reset();
     });
 
     it('getConfiguration calls', async () => {
@@ -112,7 +111,6 @@ describe('EME tracing', () => {
       const mksa = await navigator.requestMediaKeySystemAccess(
           keySystem, minimalConfigs);
       mediaKeys = await mksa.createMediaKeys();
-      emeLogger.calls.reset();
     });
 
     it('createSession calls', () => {
@@ -157,7 +155,6 @@ describe('EME tracing', () => {
           keySystem, minimalConfigs);
       const mediaKeys = await mksa.createMediaKeys();
       session = mediaKeys.createSession('temporary');
-      emeLogger.calls.reset();
     });
 
     it('generateRequest calls', async () => {
@@ -345,4 +342,66 @@ describe('EME tracing', () => {
           }));
     });
   });
+
+  describe('logs MediaKeys created via MediaCapabilities', () => {
+    const basicDecodingConfig = {
+      type: 'media-source',
+      video: {
+        contentType: 'video/mp4; codecs="avc1.42c01e"',
+        width: 256,
+        height: 110,
+        bitrate: 103942,
+        framerate: 24,
+      },
+      keySystemConfiguration: {
+        keySystem: 'com.widevine.alpha',
+        initDataType: 'cenc',
+        sessionTypes: ['temporary'],
+      },
+    };
+
+    it('decodingInfo calls', async () => {
+      const result = await navigator.mediaCapabilities.decodingInfo(
+          basicDecodingConfig);
+
+      expect(emeLogger).toHaveBeenCalledWith(
+          jasmine.objectContaining({
+            'type': TraceAnything.LogTypes.Method,
+            'className': 'MediaCapabilities',
+            'methodName': 'decodingInfo',
+            'args': [basicDecodingConfig],
+            'result': result,
+          }));
+    });
+
+    // This shows that even though the result of decodingInfo is a plain,
+    // untyped object, the TraceAnything configuration allows the engine to
+    // explore the keySystemAccess field and properly shim the EME classes that
+    // come out of decodingInfo.
+    it('MediaKeys instances', async () => {
+      const result = await navigator.mediaCapabilities.decodingInfo(
+          basicDecodingConfig);
+      expect(result.keySystemAccess).toBeTruthy();
+
+      const mediaKeys = await result.keySystemAccess.createMediaKeys();
+      const session = await mediaKeys.createSession('temporary');
+
+      expect(emeLogger).toHaveBeenCalledWith(
+          jasmine.objectContaining({
+            'type': TraceAnything.LogTypes.Method,
+            'className': 'MediaKeySystemAccess',
+            'methodName': 'createMediaKeys',
+            'args': [],
+            'result': mediaKeys,
+          }));
+      expect(emeLogger).toHaveBeenCalledWith(
+          jasmine.objectContaining({
+            'type': TraceAnything.LogTypes.Method,
+            'className': 'MediaKeys',
+            'methodName': 'createSession',
+            'args': ['temporary'],
+            'result': session,
+          }));
+    });
+  });
 });