Add metric to measure time for ModuleEntryPoint#init call.

Init is potentially heavy call which is run on the UI thread
during dynamic module loading. Add UMA to measure its execution time.

Change-Id: I09d98f8efcc7183d04846dc694516e2eeb35154f
Reviewed-on: https://chromium-review.googlesource.com/c/1291310
Commit-Queue: Anna Malova <amalova@chromium.org>
Reviewed-by: Michael van Ouwerkerk <mvanouwerkerk@chromium.org>
Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601585}

chrome/android/java/src/org/chromium/chrome/browser/customtabs/dynamicmodule/ModuleLoader.java

@@ -277,7 +277,9 @@ public class ModuleLoader {
                 crashKeys.set(CrashKeyIndex.LOADED_DYNAMIC_MODULE, mModuleId);
                 crashKeys.set(CrashKeyIndex.ACTIVE_DYNAMIC_MODULE, mModuleId);
 
+                long entryPointInitStartTime = ModuleMetrics.now();
                 entryPoint.init(moduleHost);
+                ModuleMetrics.recordEntryPointInitTime(entryPointInitStartTime);
                 ModuleMetrics.recordLoadResult(ModuleMetrics.LoadResult.SUCCESS_NEW);
                 mModuleEntryPoint = entryPoint;
                 mModuleUnusedTimeMs = ModuleMetrics.now();

chrome/android/java/src/org/chromium/chrome/browser/customtabs/dynamicmodule/ModuleMetrics.java

@@ -131,4 +131,10 @@ public final class ModuleMetrics {
                 "CustomTabs.DynamicModule.EntryPointNewInstanceTime", now() - startTime,
                 TimeUnit.MILLISECONDS);
     }
+
+    public static void recordEntryPointInitTime(long startTime) {
+        RecordHistogram.recordMediumTimesHistogram(
+                "CustomTabs.DynamicModule.EntryPointInitTime", now() - startTime,
+                TimeUnit.MILLISECONDS);
+    }
 }

tools/metrics/histograms/histograms.xml

@@ -17121,6 +17121,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="CustomTabs.DynamicModule.EntryPointInitTime" units="ms"
+    expires_after="2019-04-22">
+  <owner>amalova@chromium.org</owner>
+  <summary>
+    Time to initialize the entry point class for a custom tabs dynamic module.
+    Android only.
+  </summary>
+</histogram>
+
 <histogram name="CustomTabs.DynamicModule.EntryPointLoadClassTime" units="ms">
   <owner>mvanouwerkerk@chromium.org</owner>
   <summary>