Adds a flag to chrome:://flags to toggle touch calibration settings button in md-settings

This is required for testing to enable the feature when required.

BUG=675539
COMPONENT=About Flags, Generated Resources string

Review-Url: https://codereview.chromium.org/2640303003
Cr-Commit-Position: refs/heads/master@{#445169}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 729a319..b63540f 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2205,6 +2205,12 @@
      FEATURE_VALUE_TYPE(features::kLsdPermissionPrompt)},
 #endif
 
+#if defined(OS_CHROMEOS)
+     {"enable-touchscreen-calibration", IDS_FLAGS_TOUCHSCREEN_CALIBRATION_NAME,
+     IDS_FLAGS_TOUCHSCREEN_CALIBRATION_DESCRIPTION, kOsCrOS,
+     SINGLE_VALUE_TYPE(chromeos::switches::kEnableTouchCalibrationSetting)},
+#endif // defined(OS_CHROMEOS)
+
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.