Files.app: Add private API definition to check existance files having given md5.

The API is needed to deduplication of the photo importer feature.

BUG=450770
TEST=None
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Review URL: https://codereview.chromium.org/861363002

Cr-Commit-Position: refs/heads/master@{#312518}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index dc9d4075..df3975393 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1010,6 +1010,7 @@
   PRINTERPROVIDERINTERNAL_REPORTPRINTERCAPABILITY,
   PRINTERPROVIDERINTERNAL_REPORTPRINTERS,
   FILESYSTEMPROVIDER_GET,
+  FILEMANAGERPRIVATE_SEARCHFILESBYHASHES,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms.xml.
   ENUM_BOUNDARY