Add blink embedder APIs for DomKey conversion.

content/child/blink_platform_impl.h

Index: content/child/blink_platform_impl.h
diff --git a/content/child/blink_platform_impl.h b/content/child/blink_platform_impl.h
index dbe458d7a235506884864042075436aecb878eba..83576e24e9ee56120fc5579d201cbc1db1d798bd 100644
--- a/content/child/blink_platform_impl.h
+++ b/content/child/blink_platform_impl.h
@@ -176,6 +176,8 @@ class CONTENT_EXPORT BlinkPlatformImpl
 
   virtual blink::WebString domCodeStringFromEnum(int dom_code);
   virtual int domEnumFromCodeString(const blink::WebString& codeString);
+  virtual blink::WebString domKeyStringFromEnum(int dom_key);
+  virtual int domKeyEnumFromString(const blink::WebString& key_string);
 
  private:
   void InternalInit();