[webcryto] Validate key usages during key creation.

content/child/webcrypto/status.cc

Index: content/child/webcrypto/status.cc
diff --git a/content/child/webcrypto/status.cc b/content/child/webcrypto/status.cc
index 4fbfd709874742f69c7b412c2de030c311bee196..ad28cd78bf98045bcef40288fab2562c5e39d262 100644
--- a/content/child/webcrypto/status.cc
+++ b/content/child/webcrypto/status.cc
@@ -198,6 +198,11 @@ Status Status::ErrorGenerateKeyLength() {
                 "bits");
 }
 
+Status Status::ErrorCreateKeyBadUsages() {
+  return Status(blink::WebCryptoErrorTypeData,
+                "Cannot create key with the requested key usages");
+}
+
 Status::Status(blink::WebCryptoErrorType error_type,
                const std::string& error_details_utf8)
     : type_(TYPE_ERROR),