Files.app: Add UMA for HardUnplugged events.

The CL adds UMA for the number of seconds:

 * between HardUnplugged event and Suspend event
 * between SuspendDone event and HardUnplugged event

The numbers are needed for setting the best suppresing time for the hard
unplugged event.

BUG=433734
TEST=None

Review URL: https://codereview.chromium.org/723923004

Cr-Commit-Position: refs/heads/master@{#306523}

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

@@ -3,6 +3,7 @@
 // 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"
@@ -80,6 +81,13 @@ 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);
@@ -124,11 +132,18 @@ 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

@@ -98,6 +98,11 @@ 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

@@ -9138,6 +9138,24 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="FileBrowser.HardUnpluggedAroundSuspend.TimeSinceResume"
+    units="milliseconds">
+  <owner>hirono@chromium.org</owner>
+  <summary>
+    Chrome OS File Browser: time from the SuspendDone event to the DiskRemoved
+    event. The UMA is added temporarily for crbug.com/433734.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.HardUnpluggedAroundSuspend.TimeUntilSuspend"
+    units="milliseconds">
+  <owner>hirono@chromium.org</owner>
+  <summary>
+    Chrome OS File Browser: time from the DiskRemoved event to the Suspend
+    event. The UMA is added temporarily for crbug.com/433734.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.Load" units="milliseconds">
   <owner>joshwoodward@google.com</owner>
   <summary>