[webcryto] Validate key usages during key creation.

content/child/webcrypto/status.h

Index: content/child/webcrypto/status.h
diff --git a/content/child/webcrypto/status.h b/content/child/webcrypto/status.h
index 02f2495cb29da005379c8dbd0f22316035fcc593..8dbfce6e0c643ea11c02aef5aeb7912ef849489a 100644
--- a/content/child/webcrypto/status.h
+++ b/content/child/webcrypto/status.h
@@ -19,11 +19,6 @@ namespace webcrypto {
 //
 // As such, it is important that errors DO NOT reveal any sensitive material
 // (like key bytes).
-//
-// Care must be taken with what errors are reported back to Blink when doing
-// compound operations like unwrapping a JWK key. In this case, errors
-// generated by the JWK import are not appropriate to report since the wrapped
-// JWK is not visible to the caller.
 class CONTENT_EXPORT Status {
  public:
   Status() : type_(TYPE_ERROR) {}
@@ -187,6 +182,11 @@ class CONTENT_EXPORT Status {
   // zero, or it was not a multiple of 8 bits.
   static Status ErrorGenerateKeyLength();
 
+  // Attempted to create a key (either by importKey(), generateKey(), or
+  // unwrapKey()) however the key usages were not applicable for the key type
+  // and algorithm.
+  static Status ErrorCreateKeyBadUsages();
+
  private:
   enum Type { TYPE_ERROR, TYPE_SUCCESS };