[webcrypto] Make operations run on a background thread so they don't block the blink thread.

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 80af815ce911f6f208f12d0ec7902ab9ff2d85e0..69f40be7c4f3e374532b33b0f6a66573979e7836 100644
--- a/content/child/webcrypto/status.h
+++ b/content/child/webcrypto/status.h
@@ -20,12 +20,14 @@ 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
+// 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) {}
+
   // Returns true if the Status represents an error (any one of them).
   bool IsError() const;