Make Launch.Modes an enum histogram, not sparse.

In response to comment on crrev.com/c/2384332.

Per mpearson@: For enums versus sparses, the underlying UMA
data / logs will look the same.  It's only the implementation
in Chromium that would be different.

Change-Id: Ia75d78379977f36ec7873d5fb5d52998e6a366d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2429975Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810438}

chrome/browser/ui/startup/launch_mode_recorder.cc

@@ -148,8 +148,8 @@ void RecordLaunchModeHistogram(LaunchMode mode) {
         {base::TaskPriority::BEST_EFFORT,
          base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
         base::BindOnce([]() {
-          base::UmaHistogramSparse(kLaunchModesHistogram,
-                                   static_cast<int>(GetLaunchModeSlow()));
+          base::UmaHistogramEnumeration(kLaunchModesHistogram,
+                                        GetLaunchModeSlow());
         }));
   } else {
     base::UmaHistogramSparse(kLaunchModesHistogram, static_cast<int>(mode));

chrome/browser/ui/startup/launch_mode_recorder.h

@@ -40,6 +40,7 @@ enum class LaunchMode {
   // Launched as an installed web application in a browser tab.
   kAsWebAppInTab = 21,
   kUnknownWebApp = 22,  // The requested web application was not installed.
+  kMaxValue = 22,
 };
 
 class LaunchModeRecorder {