Remove support for the keygen tag

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 d0261c9ee7da7c44fc91fcfb29f0b993b86def8d..0deda78aef8a276a8b5e785a72453e6b1596b31a 100644
--- a/content/child/blink_platform_impl.h
+++ b/content/child/blink_platform_impl.h
@@ -73,11 +73,6 @@ class CONTENT_EXPORT BlinkPlatformImpl
       const blink::WebSecurityOrigin& origin) override;
   bool databaseSetFileSize(const blink::WebString& vfs_file_name,
                            long long size) override;
-  blink::WebString signedPublicKeyAndChallengeString(
-      unsigned key_size_index,
-      const blink::WebString& challenge,
-      const blink::WebURL& url,
-      const blink::WebURL& top_origin) override;
   size_t actualMemoryUsageMB() override;
   size_t numberOfProcessors() override;