Remove BUILD dependencies for merge_xml action

Remove BUILD dependencies for merge_xml action and list all xmls that
need to be merged in merge_xml.py instead because listing them in the
sources is too verbose as we split up smaller xmls.

Bug: 1116096
Change-Id: I1ba1e09feece3442a673d4ba41868f36e1135298
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359231
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798647}

tools/metrics/BUILD.gn

@@ -4,23 +4,9 @@
 
 action("histograms_xml") {
   script = "histograms/merge_xml.py"
-  sources = [
-    "histograms/enums.xml",
-    "histograms/histograms.xml",
-    "histograms/histograms_xml/Fingerprint/histograms.xml",
-    "histograms/histograms_xml/UMA/histograms.xml",
-    "histograms/histograms_xml/histogram_suffixes.xml",
-    "histograms/histograms_xml/obsolete_histograms.xml",
-    "ukm/ukm.xml",
-  ]
   output = "$root_out_dir/histograms.xml"
   outputs = [ output ]
-  # TODO(crbug/1116096): Automatically list all histograms paths in the
-  # sources.
-  args = rebase_path(sources, root_build_dir) + [
-           "--output",
-           rebase_path(output, root_build_dir),
-         ]
+  args = ["--output", rebase_path(output, root_build_dir)]
 }
 
 copy("actions_xml") {

tools/metrics/histograms/histogram_paths.py

@@ -39,6 +39,7 @@ ALL_XMLS_RELATIVE = [ENUMS_XML_RELATIVE, OBSOLETE_XML_RELATIVE
                      ] + HISTOGRAMS_XMLS_RELATIVE
 
 ENUMS_XML = path_util.GetInputFile(ENUMS_XML_RELATIVE)
+UKM_XML = path_util.GetInputFile('tools/metrics/ukm/ukm.xml')
 HISTOGRAMS_XMLS = [path_util.GetInputFile(f) for f in HISTOGRAMS_XMLS_RELATIVE]
 OBSOLETE_XML = path_util.GetInputFile(OBSOLETE_XML_RELATIVE)
 ALL_XMLS = [ENUMS_XML, OBSOLETE_XML] + HISTOGRAMS_XMLS

tools/metrics/histograms/merge_xml.py

@@ -13,6 +13,7 @@ import xml.dom.minidom
 import expand_owners
 import extract_histograms
 import histogram_configuration_model
+import histogram_paths
 import populate_enums
 
 
@@ -160,11 +161,16 @@ def PrettyPrintMergedFiles(filenames=[], files=[]):
 
 def main():
   parser = argparse.ArgumentParser()
-  parser.add_argument('inputs', nargs="+")
   parser.add_argument('--output', required=True)
   args = parser.parse_args()
   with open(args.output, 'w') as f:
-    f.write(PrettyPrintMergedFiles(args.inputs))
+    # This is run by
+    # https://source.chromium.org/chromium/chromium/src/+/master:tools/metrics/BUILD.gn;drc=573e48309695102dec2da1e8f806c18c3200d414;l=5
+    # to send the merged histograms.xml to the server side. Providing |UKM_XML|
+    # here is not to merge ukm.xml but to populate `UkmEventNameHash` enum
+    # values.
+    f.write(PrettyPrintMergedFiles(
+      histogram_paths.ALL_XMLS + [histogram_paths.UKM_XML]))
 
 
 if __name__ == '__main__':