[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 6d664df35056b4bd9c7697fe4feae49b9b08ff49..cc2599ebf7de09d8d0485af761b8bb3bb1ed87b7 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 a key using the specified key usages.");
+}
+
 Status::Status(blink::WebCryptoErrorType error_type,
                const std::string& error_details_utf8)
     : type_(TYPE_ERROR),