feature symfony#54855 [Stopwatch] Add getLastPeriod method to StopwatchEvent (hacfi)

This PR was merged into the 7.2 branch.

Discussion
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[Stopwatch] Add `getLastPeriod` method to `StopwatchEvent`

| Q             | A
| ------------- | ---
| Branch?       | 7.1
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

It's often useful to just get the last period (if you start and stop an event several times).

### Example
https://github.com/doctrine/migrations/blob/3.7.x/lib/Doctrine/Migrations/Version/DbalExecutor.php#L167-L168

This adds a simple `getLastPeriod` method on the `StopwatchEvent` class.

Commits
-------

5c25139 [Stopwatch] Add `getLastPeriod` method to `StopwatchEvent`

Author: fabpot

src/Symfony/Component/Stopwatch/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+7.2
+---
+
+ * Add method `getLastPeriod()` to `StopwatchEvent`
+
 5.2
 ---
 

src/Symfony/Component/Stopwatch/StopwatchEvent.php

@@ -136,6 +136,18 @@ public function getPeriods(): array
         return $this->periods;
     }
 
+    /**
+     * Gets the last event period.
+     */
+    public function getLastPeriod(): ?StopwatchPeriod
+    {
+        if ([] === $this->periods) {
+            return null;
+        }
+
+        return $this->periods[array_key_last($this->periods)];
+    }
+
     /**
      * Gets the relative time of the start of the first period in milliseconds.
      */

src/Symfony/Component/Stopwatch/StopwatchPeriod.php

@@ -12,7 +12,7 @@
 namespace Symfony\Component\Stopwatch;
 
 /**
- * Represents an Period for an Event.
+ * Represents a Period for an Event.
  *
  * @author Fabien Potencier <[email protected]>
  */