media: Add UMA to record time to GenerateRequest and LoadSession

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 948db9bd8d872eeea0b85076d89bd5efcc541c69..e3668a74bccd70b45b485fdf5de37a411d1e2b39 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -25275,6 +25275,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>KeyError event count using the Clear Key key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.ClearKey.TimeTo" units="ms">
+  <owner>xhwang@chromium.org</owner>
+  <summary>
+    The time it takes to resolve a CDM promise for Clear Key key system.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.KeySystemSupport.Widevine"
     enum="MediaKeySystemSupportStatus">
   <obsolete>
@@ -25370,6 +25377,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>System code count using an unknown key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.Unknown.TimeTo" units="ms">
+  <owner>xhwang@chromium.org</owner>
+  <summary>
+    The time it takes to resolve a CDM promise for an unknown key system.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.Widevine" enum="CdmPromiseResult">
   <owner>sandersd@chromium.org</owner>
   <summary>
@@ -25431,6 +25445,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>System code count using the Widevine key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.Widevine.TimeTo" units="ms">
+  <owner>xhwang@chromium.org</owner>
+  <summary>
+    The time it takes to resolve a CDM promise for the Widevine key system.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.Widevine.VideoCapability.HasEmptyRobustness"
     enum="BooleanEmpty">
   <owner>xhwang@chromium.org</owner>
@@ -113443,6 +113464,14 @@ value.
   <affected-histogram name="Media.EME.Widevine"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="EmeTimeToResolvePromise" separator=".">
+  <suffix name="GenerateRequest" label="GenerateRequest promises only."/>
+  <suffix name="LoadSession" label="LoadSession promises only."/>
+  <affected-histogram name="Media.EME.ClearKey.TimeTo"/>
+  <affected-histogram name="Media.EME.Unknown.TimeTo"/>
+  <affected-histogram name="Media.EME.Widevine.TimeTo"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="EngagementScoreBuckets">
   <owner>calamity@chromium.org</owner>
   <suffix name="0"/>