[cg.workflow] Update str(ProcessorRecord) (#5012)

These should be good for e.g. plot legends

cirq-google/cirq_google/workflow/processor_record.py

@@ -70,6 +70,9 @@ def get_processor(self) -> 'cg.EngineProcessor':
     def __repr__(self):
         return dataclass_repr(self, namespace='cirq_google')
 
+    def __str__(self) -> str:
+        return self.processor_id
+
     @classmethod
     def _json_namespace_(cls) -> str:
         return 'cirq.google'
@@ -143,7 +146,7 @@ def __str__(self) -> str:
         elif self.noise_strength == float('inf'):
             suffix = 'zeros'
         else:
-            suffix = f'p={self.noise_strength:.3e}'
+            suffix = f'depol({self.noise_strength:.3e})'
         return f'{self.processor_id}-{suffix}'
 
     def __repr__(self) -> str:

cirq-google/cirq_google/workflow/processor_record_test.py

@@ -86,6 +86,7 @@ def test_engine_backend(get_processor, _):
         assert isinstance(proc_rec.get_sampler(), cirq.Sampler)
         assert isinstance(proc_rec.get_device(), cirq.Device)
     cirq.testing.assert_equivalent_repr(proc_rec, global_vals={'cirq_google': cg})
+    assert str(proc_rec) == 'rainbow'
 
 
 @mock.patch('cirq_google.engine.client.quantum.QuantumEngineServiceClient')
@@ -124,7 +125,7 @@ def test_simulated_backend_descriptive_name():
     assert isinstance(p.get_sampler(), cirq.Simulator)
 
     p = cg.SimulatedProcessorWithLocalDeviceRecord('rainbow', noise_strength=1e-3)
-    assert str(p) == 'rainbow-p=1.000e-03'
+    assert str(p) == 'rainbow-depol(1.000e-03)'
     assert isinstance(p.get_sampler(), cirq.DensityMatrixSimulator)
 
     p = cg.SimulatedProcessorWithLocalDeviceRecord('rainbow', noise_strength=float('inf'))