Revert "Files.app: Add UMA for HardUnplugged events."

We no longer need these UMA.
This reverts commit 7f60d255.

BUG=433734
TEST=None

Review URL: https://codereview.chromium.org/888083004

Cr-Commit-Position: refs/heads/master@{#314968}

chrome/browser/chromeos/extensions/file_manager/device_event_router.cc

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 #include "base/bind.h"
-#include "base/metrics/histogram_macros.h"
 #include "base/thread_task_runner_handle.h"
 #include "chrome/browser/chromeos/extensions/file_manager/device_event_router.h"
 #include "chrome/browser/chromeos/file_manager/volume_manager.h"
@@ -81,13 +80,6 @@ void DeviceEventRouter::OnDiskRemoved(
   const std::string& device_path = disk.system_path_prefix();
   if (!disk.mount_path().empty() &&
       GetDeviceState(device_path) != DEVICE_HARD_UNPLUGGED_AND_REPORTED) {
-    // TODO(hirono): Remove the temporary UMA.  crbug.com/433734
-    if (!last_suspend_done_.is_null()) {
-      UMA_HISTOGRAM_MEDIUM_TIMES(
-          "FileBrowser.HardUnpluggedAroundSuspend.TimeSinceResume",
-          base::Time::Now() - last_suspend_done_);
-    }
-    last_hard_unplugged_ = base::Time::Now();
     OnDeviceEvent(file_manager_private::DEVICE_EVENT_TYPE_HARD_UNPLUGGED,
                   device_path);
     SetDeviceState(device_path, DEVICE_HARD_UNPLUGGED_AND_REPORTED);
@@ -132,18 +124,11 @@ void DeviceEventRouter::OnFormatCompleted(const std::string& device_path,
 
 void DeviceEventRouter::SuspendImminent() {
   DCHECK(thread_checker_.CalledOnValidThread());
-  // TODO(hirono): Remove the temporary UMA.  crbug.com/433734
-  if (!last_hard_unplugged_.is_null()) {
-    UMA_HISTOGRAM_MEDIUM_TIMES(
-        "FileBrowser.HardUnpluggedAroundSuspend.TimeUntilSuspend",
-        base::Time::Now() - last_hard_unplugged_);
-  }
   is_resuming_ = true;
 }
 
 void DeviceEventRouter::SuspendDone(const base::TimeDelta& sleep_duration) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  last_suspend_done_ = base::Time::Now();
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&DeviceEventRouter::SuspendDoneDelayed,

chrome/browser/chromeos/extensions/file_manager/device_event_router.h

@@ -96,11 +96,6 @@ class DeviceEventRouter : public VolumeManagerObserver,
   // Thread checker.
   base::ThreadChecker thread_checker_;
 
-  // Last event time for UMA.
-  // TODO(hirono): Remove the temporarily UMA.  crbug.com/433734
-  base::Time last_hard_unplugged_;
-  base::Time last_suspend_done_;
-
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate the weak pointers before any other members are destroyed.
   base::WeakPtrFactory<DeviceEventRouter> weak_factory_;

tools/metrics/histograms/histograms.xml

@@ -9509,6 +9509,9 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 
 <histogram name="FileBrowser.HardUnpluggedAroundSuspend.TimeSinceResume"
     units="milliseconds">
+  <obsolete>
+    The bug which the UMA was investigating got fixed.
+  </obsolete>
   <owner>hirono@chromium.org</owner>
   <summary>
     Chrome OS File Browser: time from the SuspendDone event to the DiskRemoved
@@ -9518,6 +9521,9 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 
 <histogram name="FileBrowser.HardUnpluggedAroundSuspend.TimeUntilSuspend"
     units="milliseconds">
+  <obsolete>
+    The bug which the UMA was investigating got fixed.
+  </obsolete>
   <owner>hirono@chromium.org</owner>
   <summary>
     Chrome OS File Browser: time from the DiskRemoved event to the Suspend