Add histograms presubmit check for UseCounter.h

third_party/WebKit/Source/core/frame/PRESUBMIT.py

Index: third_party/WebKit/Source/core/frame/PRESUBMIT.py
diff --git a/third_party/WebKit/Source/core/frame/PRESUBMIT.py b/third_party/WebKit/Source/core/frame/PRESUBMIT.py
index eba4c2f66424070ec1a33f4ddb8ae72efd61c7ba..67c2ee8d78ee2c2a3b3eb6efafd59171cd2f0ae0 100644
--- a/third_party/WebKit/Source/core/frame/PRESUBMIT.py
+++ b/third_party/WebKit/Source/core/frame/PRESUBMIT.py
@@ -49,9 +49,51 @@ def _RunUseCounterChecks(input_api, output_api):
     return []
 
 
+def _RunUmaHistogramChecks(input_api, output_api):
+    import sys
+
+    original_sys_path = sys.path
+    try:
+        sys.path = sys.path + [input_api.os_path.join(
+            input_api.PresubmitLocalPath(), '..', '..', '..', '..', '..',
+            'tools', 'metrics', 'histograms')]
+        import update_histogram_enum
+    finally:
+        sys.path = original_sys_path
+
+    source_path = ''
+    for f in input_api.AffectedFiles():
+        if f.LocalPath().endswith('UseCounter.h'):
+            source_path = f.LocalPath()
+            break
+    else:
+        return []
+
+    START_MARKER = '^enum Feature {'
+    END_MARKER = '^NumberOfFeatures'
+    if update_histogram_enum.HistogramNeedsUpdate(
+            histogram_enum_name='FeatureObserver',
+            source_enum_path=source_path,
+            start_marker=START_MARKER,
+            end_marker=END_MARKER):
+        return [output_api.PresubmitPromptWarning(
+            'UseCounter::Feature has been updated and the UMA mapping needs to '
+            'be regenerated. Please run update_use_counter_feature_enum.py in '
+            'src/tools/metrics/histograms/ to update the mapping.',
+            items=[source_path])]
+
+    return []
+
+
 def CheckChangeOnUpload(input_api, output_api):
-    return _RunUseCounterChecks(input_api, output_api)
+    results = []
+    results.extend(_RunUseCounterChecks(input_api, output_api))
+    results.extend(_RunUmaHistogramChecks(input_api, output_api))
+    return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
-    return _RunUseCounterChecks(input_api, output_api)
+    results = []
+    results.extend(_RunUseCounterChecks(input_api, output_api))
+    results.extend(_RunUmaHistogramChecks(input_api, output_api))
+    return results