metrics: Split up chrome vs. chromeos histograms.xml files

Move the ChromeOS.* prefixed metrics into their own file/directory.
Most of these metrics are not general Chrome browser metrics, and this
will let us have a separate OWNERS file once we train up some
reviewers.

Bug: none
Change-Id: If42613c021c44e0e0639ec68db6f012416046c6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446519
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Auto-Submit: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814122}

chrome/browser/metrics/BUILD.gn

@@ -46,6 +46,7 @@ generate_expired_histograms_array("expired_histograms_array") {
     "//tools/metrics/histograms/histograms_xml/bluetooth/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/browser/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/chrome/histograms.xml",
+    "//tools/metrics/histograms/histograms_xml/chromeos/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/cloud/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/compositing/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/content/histograms.xml",

ios/chrome/browser/metrics/BUILD.gn

@@ -299,6 +299,7 @@ generate_expired_histograms_array("expired_histograms_array") {
     "//tools/metrics/histograms/histograms_xml/bluetooth/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/browser/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/chrome/histograms.xml",
+    "//tools/metrics/histograms/histograms_xml/chromeos/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/cloud/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/compositing/histograms.xml",
     "//tools/metrics/histograms/histograms_xml/content/histograms.xml",

tools/metrics/histograms/histograms_index.txt

@@ -14,6 +14,7 @@ tools/metrics/histograms/histograms_xml/blink/histograms.xml
 tools/metrics/histograms/histograms_xml/bluetooth/histograms.xml
 tools/metrics/histograms/histograms_xml/browser/histograms.xml
 tools/metrics/histograms/histograms_xml/chrome/histograms.xml
+tools/metrics/histograms/histograms_xml/chromeos/histograms.xml
 tools/metrics/histograms/histograms_xml/cloud/histograms.xml
 tools/metrics/histograms/histograms_xml/compositing/histograms.xml
 tools/metrics/histograms/histograms_xml/content/histograms.xml

tools/metrics/histograms/split_xml.py

@@ -44,6 +44,7 @@ AGGREGATE_THRESHOLD = 20
 # put in.
 _PREDEFINED_NAMES_MAPPING = {
     'BackForwardCache': 'BackForwardCache',
+    'ChromeOS': 'ChromeOS',
     'CustomTabs': 'CustomTabs',
     'CustomTab': 'CustomTabs',
     'DataReductionProxy': 'DataReductionProxy',