cros: Add UMA metrics in encryption migration UI.

chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc
index d655542a21fdfab84a781bb9927df3cf55a9ed5e..1b9185ded464ce299832fae502c3d46c6a169347 100644
--- a/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc
@@ -4,12 +4,14 @@
 
 #include "chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h"
 
+#include <cmath>
 #include <string>
 #include <utility>
 
 #include "ash/system/devicetype_utils.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/sys_info.h"
 #include "base/task_scheduler/post_task.h"
 #include "chrome/browser/browser_process.h"
@@ -46,6 +48,31 @@ constexpr char kJsApiStartMigration[] = "startMigration";
 constexpr char kJsApiSkipMigration[] = "skipMigration";
 constexpr char kJsApiRequestRestart[] = "requestRestart";
 
+// UMA names.
+constexpr char kUmaNameFirstScreen[] = "Cryptohome.MigrationUI.FirstScreen";
+constexpr char kUmaNameUserChoice[] = "Cryptohome.MigrationUI.UserChoice";
+constexpr char kUmaNameConsumedBatteryPercent[] =
+    "Cryptohome.MigrationUI.ConsumedBatteryPercent";
+
+// This enum must match the numbering for Cryptohome.MigrationUI.FirstScreen in
+// histograms.xml. Do not reorder or remove items, only add new items before
+// FIRST_SCREEN_MAX.
+enum FirstScreen {

[Ilya Sherman, 2017/04/28 21:07:52]

Optional nit: Mebbe use enum class here?

[fukino, 2017/04/29 14:40:31]

Done.

+  FIRST_SCREEN_READY = 0,
+  FIRST_SCREEN_RESUME = 1,
+  FIRST_SCREEN_LOW_STORAGE = 2,
+  FIRST_SCREEN_MAX

[Ilya Sherman, 2017/04/28 21:07:52]

Optional nit: Typically, "MAX" is used as an alias to the last item in the enum;
and "COUNT" is used to count the number of elements in the enum.  So, I'd rename
this to COUNT.

[fukino, 2017/04/29 14:40:31]

Agreed. Done.

+};
+
+// This enum must match the numbering for Cryptohome.MigrationUI.UserChoice in
+// histograms.xml. Do not reorder or remove items, only add new items before
+// FIRST_SCREEN_MAX.
+enum UserChoice {
+  USER_CHOICE_UPDATE = 0,
+  USER_CHOICE_SKIP = 1,
+  USER_CHOICE_MAX
+};
+
 bool IsTestingUI() {
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       chromeos::switches::kTestEncryptionMigrationUI);
@@ -187,10 +214,14 @@ void EncryptionMigrationScreenHandler::PowerChanged(
 }
 
 void EncryptionMigrationScreenHandler::HandleStartMigration() {
+  UMA_HISTOGRAM_ENUMERATION(kUmaNameUserChoice, USER_CHOICE_UPDATE,
+                            USER_CHOICE_MAX);
   WaitBatteryAndMigrate();
 }
 
 void EncryptionMigrationScreenHandler::HandleSkipMigration() {
+  UMA_HISTOGRAM_ENUMERATION(kUmaNameUserChoice, USER_CHOICE_SKIP,

[Ilya Sherman, 2017/04/28 21:07:51]

Please create a small wrapper function for recording metrics to this histogram. 
The UMA_HISTOGRAM macros expand to a nontrivial amount of code, so it's nice to
help the compiler avoid duplication of that code by wrapping it up in a single
call-site per histogram.

[fukino, 2017/04/29 14:40:31]

Done.

+                            USER_CHOICE_MAX);
   // If the user skips migration, we mount the cryptohome without performing the
   // migration by reusing UserContext and LoginPerformer which were used in the
   // previous attempt and dropping |is_forcing_dircrypto| flag in UserContext.
@@ -239,11 +270,17 @@ void EncryptionMigrationScreenHandler::CheckAvailableStorage() {
 void EncryptionMigrationScreenHandler::OnGetAvailableStorage(int64_t size) {
   if (size >= kMinimumAvailableStorage || IsTestingUI()) {
     if (should_resume_) {
+      UMA_HISTOGRAM_ENUMERATION(kUmaNameFirstScreen, FIRST_SCREEN_RESUME,
+                                FIRST_SCREEN_MAX);
       WaitBatteryAndMigrate();
     } else {
+      UMA_HISTOGRAM_ENUMERATION(kUmaNameFirstScreen, FIRST_SCREEN_READY,
+                                FIRST_SCREEN_MAX);
       UpdateUIState(UIState::READY);
     }
   } else {
+    UMA_HISTOGRAM_ENUMERATION(kUmaNameFirstScreen, FIRST_SCREEN_LOW_STORAGE,
+                              FIRST_SCREEN_MAX);

[Ilya Sherman, 2017/04/28 21:07:52]

For this histogram, you could simply set the metric in the if/else branches, and
then log it at the bottom of this function.

[fukino, 2017/04/29 14:40:31]

I added a wrapper function for consistency with UserChoice.

     CallJS("setAvailableSpaceInString", ui::FormatBytes(size));
     CallJS("setNecessarySpaceInString",
            ui::FormatBytes(kMinimumAvailableStorage));
@@ -264,6 +301,7 @@ void EncryptionMigrationScreenHandler::WaitBatteryAndMigrate() {
 
 void EncryptionMigrationScreenHandler::StartMigration() {
   UpdateUIState(UIState::MIGRATING);
+  initial_battery_percent_ = current_battery_percent_;
 
   // Mount the existing eCryptfs vault to a temporary location for migration.
   cryptohome::MountParameters mount(false);
@@ -362,6 +400,14 @@ void EncryptionMigrationScreenHandler::OnMigrationProgress(
       CallJS("setMigrationProgress", static_cast<double>(current) / total);
       break;
     case cryptohome::DIRCRYPTO_MIGRATION_SUCCESS:
+      // If the battery level decreased during migration, record the consumed
+      // battery level.
+      if (current_battery_percent_ < initial_battery_percent_) {
+        UMA_HISTOGRAM_PERCENTAGE(
+            kUmaNameConsumedBatteryPercent,
+            static_cast<int>(std::round(initial_battery_percent_ -
+                                        current_battery_percent_)));
+      }
       // Restart immediately after successful migration.
       DBusThreadManager::Get()->GetPowerManagerClient()->RequestRestart();
       break;