Re-add support for the components tag and OWNERS expansion.

This is done by updating the histograms config model and by uncommenting
the call to ExpandHistogramsOWNERS() in merge_xml.py. This ensures
<owner>src/dir/OWNERS</owner> is expanded into actual owners, e.g.
<owner>name1@google.com</owner> and <owner>name2@chromium.org</owner>.
Uncommenting this allows components to be extracted from OWNERS files as
well. That way, component info, if available in an OWNERS file, is added
to histogram expiry bugs, e.g. http://crbug/1088985.

Also, add component documentation and add a component to two
Variations.Headers.* histograms.

Support was previously added for component tags, see http://crbug/989112
for details, but it wasn't explicitly used.

Bug: 1133699
Change-Id: I572c877be8929923fd14df352e762a7a293ca5ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2442136Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#813914}

tools/metrics/histograms/README.md

@@ -516,6 +516,19 @@ usefulness. When a histogram is nearing expiry, a robot will file a reminder
 bug in Monorail. It's important that somebody familiar with the histogram
 notices and triages such bugs!
 
+### Components
+
+Histograms may be associated with components, which can help make sure that
+histogram expiry bugs don't fall through the cracks.
+
+There are two ways in which components may be associated with a histogram. The
+first and recommended way is to add a tag to a histogram or histogram suffix,
+e.g. <component>UI&gt;Shell</component>. The second way is to specify an OWNERS
+file as a secondary owner for a histogram. If the OWNERS file contains a
+component, then the component is associated with the histogram. If the specified
+OWNERS file doesn't have a component, but an OWNERS file in a parent directory
+does, then the parent directory's component is used.
+
 ### Cleaning Up Histogram Entries
 
 Do not delete histograms from histograms.xml. Instead, mark unused

tools/metrics/histograms/extract_histograms.py

@@ -370,6 +370,29 @@ def _ExtractOwners(node):
   return owners, has_owner
 
 
+def _ExtractComponents(histogram):
+  """Extracts component information from the given histogram element.
+
+  Components are present when a histogram has a component tag, e.g.
+  <component>UI&gt;Browser</component>. Components may also be present when an
+  OWNERS file is given as a histogram owner, e.g. <owner>src/dir/OWNERS</owner>.
+  See _ExtractComponentFromOWNERS() in the following file for details:
+  chromium/src/tools/metrics/histograms/expand_owners.py.
+
+  Args:
+    histogram: A DOM Element corresponding to a histogram.
+
+  Returns:
+    A list of the components associated with the histogram, e.g.
+    ['UI>Browser>Spellcheck'].
+  """
+  component_nodes = histogram.getElementsByTagName('component')
+  return [
+      _GetTextFromChildNodes(component_node)
+      for component_node in component_nodes
+  ]
+
+
 def _ValidateDateString(date_str):
   """Checks if |date_str| matches 'YYYY-MM-DD'.
 
@@ -553,6 +576,11 @@ def _ExtractHistogramsFromXmlTree(tree, enums):
     if owners:
       histogram_entry['owners'] = owners
 
+    # Find <component> tag.
+    components = _ExtractComponents(histogram)
+    if components:
+      histogram_entry['components'] = components
+
     # Find <summary> tag.
     summary_nodes = list(IterElementsWithTag(histogram, 'summary'))
 

tools/metrics/histograms/extract_histograms_test.py

@@ -445,6 +445,33 @@ class ExtractHistogramsTest(unittest.TestCase):
         'Multi-paragraph sample description UI>Browser. Words.\n\n'
         'Still multi-paragraph sample description.\n\nHere.')
 
+  def testComponentExtraction(self):
+    """Checks that components are successfully extracted from histograms."""
+    histogram = xml.dom.minidom.parseString("""
+<histogram-configuration>
+<histograms>
+  <histogram name="Coffee" expires_after="2022-01-01">
+    <owner>histogram_owner@google.com</owner>
+    <summary>An ode to coffee.</summary>
+    <component>Liquid&gt;Hot</component>
+    <component>Caffeine</component>
+  </histogram>
+</histograms>
+
+<histogram_suffixes_list>
+  <histogram_suffixes name="Brand" separator=".">
+    <suffix name="Dunkies" label="The coffee is from Dunkin."/>
+    <affected-histogram name="Coffee"/>
+  </histogram_suffixes>
+</histogram_suffixes_list>
+</histogram-configuration>
+""")
+    histograms, _ = extract_histograms.ExtractHistogramsFromDom(histogram)
+    self.assertEqual(histograms['Coffee']['components'],
+                     ['Liquid>Hot', 'Caffeine'])
+    self.assertEqual(histograms['Coffee.Dunkies']['components'],
+                     ['Liquid>Hot', 'Caffeine'])
+
   def testNewHistogramWithoutSummary(self):
     histogram_without_summary = xml.dom.minidom.parseString("""
 <histogram-configuration>

tools/metrics/histograms/histogram_configuration_model.py

@@ -12,6 +12,7 @@ import models
 
 _OBSOLETE_TYPE = models.TextNodeType('obsolete')
 _OWNER_TYPE = models.TextNodeType('owner', single_line=True)
+_COMPONENT_TYPE = models.TextNodeType('component', single_line=True)
 _SUMMARY_TYPE = models.TextNodeType('summary', single_line=True)
 _DETAILS_TYPE = models.TextNodeType('details')
 
@@ -142,6 +143,7 @@ _HISTOGRAM_TYPE = models.ObjectNodeType(
     alphabetization=[
         (_OBSOLETE_TYPE.tag, _KEEP_ORDER),
         (_OWNER_TYPE.tag, _KEEP_ORDER),
+        (_COMPONENT_TYPE.tag, _KEEP_ORDER),
         (_SUMMARY_TYPE.tag, _KEEP_ORDER),
         (_DETAILS_TYPE.tag, _KEEP_ORDER),
         (_TOKEN_TYPE.tag, _KEEP_ORDER),
@@ -150,6 +152,7 @@ _HISTOGRAM_TYPE = models.ObjectNodeType(
     children=[
         models.ChildType(_OBSOLETE_TYPE.tag, _OBSOLETE_TYPE, multiple=False),
         models.ChildType(_OWNER_TYPE.tag, _OWNER_TYPE, multiple=True),
+        models.ChildType(_COMPONENT_TYPE.tag, _COMPONENT_TYPE, multiple=True),
         models.ChildType(_SUMMARY_TYPE.tag, _SUMMARY_TYPE, multiple=False),
         models.ChildType(_DETAILS_TYPE.tag, _DETAILS_TYPE, multiple=False),
         models.ChildType(_TOKEN_TYPE.tag, _TOKEN_TYPE, multiple=True),

tools/metrics/histograms/histogram_configuration_model_test_histograms.py

@@ -84,6 +84,7 @@ PRETTY_XML = """
   </obsolete>
   <owner>owner1@chromium.org</owner>
   <owner>owner2@chromium.org</owner>
+  <component>Component&gt;Subcomponent</component>
   <summary>Summary text</summary>
 </histogram>
 
@@ -119,6 +120,7 @@ XML_WRONG_ATTRIBUTE_ORDER = """
   </obsolete>
   <owner>owner1@chromium.org</owner>
   <owner>owner2@chromium.org</owner>
+  <component>Component&gt;Subcomponent</component>
   <summary>Summary text</summary>
 </histogram>
 
@@ -189,6 +191,7 @@ XML_WRONG_INDENT = """
     </obsolete>
       <owner>owner1@chromium.org</owner>
       <owner>owner2@chromium.org</owner>
+      <component>Component&gt;Subcomponent</component>
     <summary>Summary text</summary>
   </histogram>
 
@@ -224,6 +227,9 @@ XML_WRONG_SINGLELINE = """
     owner1@chromium.org
   </owner>
   <owner>owner2@chromium.org</owner>
+  <component>
+    Component&gt;Subcomponent
+  </component>
   <summary>
     Summary text
   </summary>
@@ -259,6 +265,7 @@ XML_WRONG_LINEBREAK = """
   </obsolete>
   <owner>owner1@chromium.org</owner>
   <owner>owner2@chromium.org</owner>
+  <component>Component&gt;Subcomponent</component>
   <summary>Summary text</summary>
 
 </histogram>
@@ -292,6 +299,7 @@ XML_WRONG_CHILDREN_ORDER = """
   </obsolete>
   <summary>Summary text</summary>
   <owner>owner1@chromium.org</owner>
+  <component>Component&gt;Subcomponent</component>
   <owner>owner2@chromium.org</owner>
 </histogram>
 

tools/metrics/histograms/histograms_xml/variations/histograms.xml

@@ -121,6 +121,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
     expires_after="2020-12-15">
   <owner>caitlinfischer@google.com</owner>
   <owner>src/base/metrics/OWNERS</owner>
+  <component>Internals&gt;Metrics</component>
   <summary>
     The owner of the top-level domain from which certain subframe-initiated HTTP
     requests are made. It's logged after determining that (i) the request should
@@ -148,6 +149,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>jwd@chromium.org</owner>
   <owner>caitlinfischer@google.com</owner>
   <owner>src/base/metrics/OWNERS</owner>
+  <component>Internals&gt;Metrics</component>
   <summary>
     Details about the request context in which an HTTP request is made. Logged
     after determining that the request should include variations headers but