Summary tag should not be empty

The summary child in the histogram tag should not be empty.

Change-Id: I7030df527b7852bd36de9e37ab48d09fca600d51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422985
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810015}

tools/metrics/histograms/extract_histograms.py

@@ -567,8 +567,9 @@ def _ExtractHistogramsFromXmlTree(tree, enums):
       reason = _GetTextFromChildNodes(obsolete_nodes[0])
       histogram_entry['obsolete'] = reason
 
-    # Non-obsolete histograms should provide a <summary>.
-    if not obsolete_nodes and not summary_nodes:
+    # Non-obsolete histograms should provide a non-empty <summary>.
+    if not obsolete_nodes and (not summary_nodes or
+                               not histogram_entry['summary']):
       logging.error('histogram %s should provide a <summary>', name)
       have_errors = True
 

tools/metrics/histograms/extract_histograms_test.py

@@ -459,6 +459,21 @@ class ExtractHistogramsTest(unittest.TestCase):
         histogram_without_summary, {})
     self.assertTrue(have_errors)
 
+  def testNewHistogramWithEmptySummary(self):
+    histogram_with_empty_summary = xml.dom.minidom.parseString("""
+<histogram-configuration>
+<histograms>
+ <histogram name="Test.Histogram" units="things" expires_after="2019-01-01">
+   <owner>person@chromium.org</owner>
+   <summary/>
+ </histogram>
+</histograms>
+</histogram-configuration>
+""")
+    _, have_errors = extract_histograms._ExtractHistogramsFromXmlTree(
+        histogram_with_empty_summary, {})
+    self.assertTrue(have_errors)
+
   def testNewHistogramWithoutEnumOrUnit(self):
     histogram_without_enum_or_unit = xml.dom.minidom.parseString("""
 <histogram-configuration>