[webnfc] Add WebNFC feature flag

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 456522f7be5e0967c3375a3b69d9d8f180430f4d..55758809f4e0185e3e36a01358e8be7b21c126bc 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -103243,6 +103243,7 @@ from previous Chrome versions.
   <int value="-344343842" label="disable-experimental-app-list"/>
   <int value="-340622848" label="disable-javascript-harmony-shipping"/>
   <int value="-340255045" label="allow-nacl-socket-api"/>
+  <int value="-340023285" label="WebNFC:enabled"/>
   <int value="-329727402" label="disable-files-quick-view"/>
   <int value="-328361990" label="enable-experimental-extension-apis"/>
   <int value="-323831744" label="token-binding:enabled"/>
@@ -103441,6 +103442,7 @@ from previous Chrome versions.
   <int value="494733611" label="disable-drop-sync-credential"/>
   <int value="503245473" label="disable-translate-new-ux"/>
   <int value="504994663" label="GenericSensor:disabled"/>
+  <int value="506680761" label="WebNFC:disabled"/>
   <int value="510814146" label="OfflineBookmarks:enabled"/>
   <int value="535976218" label="enable-plugin-power-saver"/>
   <int value="538468149" label="OfflinePagesCT:enabled"/>