Revert "Make Launch.Modes an enum histogram, not sparse."

This reverts commit 085b583f.

Reason for revert: <crbug.com/1132543>

Original change's description:
> 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/+/2429975
> Reviewed-by: Peter Boström <pbos@chromium.org>
> Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#810438}

TBR=pbos@chromium.org,davidbienvenu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Ia7edc131b855a4ceb384b8e2d76055386d1044c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2433060Reviewed-by: David Bienvenu <davidbienvenu@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811005}

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::UmaHistogramEnumeration(kLaunchModesHistogram,
-                                        GetLaunchModeSlow());
+          base::UmaHistogramSparse(kLaunchModesHistogram,
+                                   static_cast<int>(GetLaunchModeSlow()));
         }));
   } else {
     base::UmaHistogramSparse(kLaunchModesHistogram, static_cast<int>(mode));

chrome/browser/ui/startup/launch_mode_recorder.h

@@ -40,7 +40,6 @@ 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 {