Add deprecation message for -webkit-background-composite

third_party/WebKit/Source/core/frame/UseCounter.h

Index: third_party/WebKit/Source/core/frame/UseCounter.h
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.h b/third_party/WebKit/Source/core/frame/UseCounter.h
index 11ebf3cbb33dbf53668a935d050d4124693d2908..b0b89d051898f8d876353d314d46c99b7fcdf3c8 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -991,12 +991,17 @@ public:
     static void countDeprecation(const LocalFrame*, Feature);
     static void countDeprecation(ExecutionContext*, Feature);
     static void countDeprecation(const Document&, Feature);
+
+    static void showDeprecationWarning(const LocalFrame*, CSSPropertyID);
     // Use countDeprecationIfNotPrivateScript() instead of countDeprecation()
     // if you don't want to count metrics in private scripts. You should use
     // countDeprecationIfNotPrivateScript() in a binding layer.
     static void countDeprecationIfNotPrivateScript(v8::Isolate*, ExecutionContext*, Feature);
     static String deprecationMessage(Feature);
 
+    // CSSPropertyIDs that aren't deprecated don't have a deprecation message.

[alancutter (OOO until 2018), 2016/01/20 00:58:27]

// CSSPropertyIDs that aren't deprecated return an empty string.

+    static String deprecationMessage(CSSPropertyID);
+
     // Return whether the Feature was previously counted for this document.
     // NOTE: only for use in testing.
     static bool isCounted(Document&, Feature);