Auto merge of #13091 - zack1030:issue-12792, r=shinglyu

Create ./mach test-perf command

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---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [X] These changes fix #12792 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because it is low-risk

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in **testing_commands.py**, I linked the new command to **test_perf.sh**
in **test_perf.sh**, it prepares tp5n.zip and virtual environment
then runs **test_all.sh**

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python/servo/testing_commands.py

@@ -169,6 +169,16 @@ class MachCommands(CommandBase):
 
         return call(["cargo", "test"], env=env, cwd=path.join("ports", "geckolib"))
 
+    @Command('test-perf',
+             description='Run the page load performance test',
+             category='testing')
+    def test_perf(self):
+        self.ensure_bootstrapped()
+        env = self.build_env()
+        return call(["bash", "test_perf.sh"],
+                    env=env,
+                    cwd=path.join("etc", "ci", "performance"))
+
     @Command('test-unit',
              description='Run unit tests',
              category='testing')