Add metrics for Chrome OS grammar check service in histograms.xml.

The metrics were added in https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2497369

Bug: 1132699
Change-Id: Ice9f49732f3daf682a7ac60838f061de2f5fecea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521976
Commit-Queue: Jing Wang <jiwan@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831248}

tools/metrics/histograms/enums.xml

@@ -46381,6 +46381,11 @@ from previous Chrome versions.
   <int value="9" label="EXECUTION_ERROR"/>
 </enum>
 
+<enum name="MachineLearningServiceGrammarCheckResultEvent">
+  <int value="0" label="OK"/>
+  <int value="1" label="ERROR"/>
+</enum>
+
 <enum name="MachineLearningServiceLoadHandwritingModelResultEvent">
   <int value="0" label="OK"/>
   <int value="1" label="DEPRECATED_MODEL_SPEC_ERROR"/>

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -8427,6 +8427,25 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="MachineLearningService.GrammarChecker.Check.Event"
+    enum="Boolean" expires_after="2021-12-31">
+  <owner>jiwan@chromium.org</owner>
+  <owner>amoylan@chromium.org</owner>
+  <summary>The result of grammar check, which can be OK or ERROR.</summary>
+</histogram>
+
+<histogram name="MachineLearningService.GrammarChecker.LoadModelResult.Event"
+    enum="MachineLearningServiceLoadModelResultEvent"
+    expires_after="2021-12-31">
+  <owner>jiwan@chromium.org</owner>
+  <owner>amoylan@chromium.org</owner>
+  <summary>
+    The result of load grammar model, which can be OK or some specific error.
+    The error code could be logged in machine learning service in chrome or in
+    chromeos when grammar model is not loaded successfully.
+  </summary>
+</histogram>
+
 <histogram name="MachineLearningService.HandwritingModel.LoadModelResult.Event"
     enum="MachineLearningServiceLoadHandwritingModelResultEvent"
     expires_after="2021-04-25">