[On-device adaptive brightness] Add a flag to control auto screen brightness model.

Bug: 881215
Test: unit_tests --gtest_filter=AboutFlagsTest*, AboutFlagsHistogramTest*
Change-Id: Ia1749065e2b41bba2f402d7790e9e00d7592b144
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610666
Commit-Queue: Jia Meng <[email protected]>
Reviewed-by: Andrew Moylan <[email protected]>
Cr-Commit-Position: refs/heads/master@{#659748}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 9573ea7a..036d5c5 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -141,6 +141,9 @@
 extern const char kAutofillUseImprovedLabelDisambiguationName[];
 extern const char kAutofillUseImprovedLabelDisambiguationDescription[];
 
+extern const char kAutoScreenBrightnessName[];
+extern const char kAutoScreenBrightnessDescription[];
+
 extern const char kAwaitOptimizationName[];
 extern const char kAwaitOptimizationDescription[];