[webcrypto] Add RSA public key SPKI import/export for NSS.

content/renderer/webcrypto/webcrypto_impl.h

Index: content/renderer/webcrypto/webcrypto_impl.h
diff --git a/content/renderer/webcrypto/webcrypto_impl.h b/content/renderer/webcrypto/webcrypto_impl.h
index 6c6a6b06887f66298093a6afffc64bab99eecd2e..b194c9f6a1211c2b7902c78648072a295a20c1dc 100644
--- a/content/renderer/webcrypto/webcrypto_impl.h
+++ b/content/renderer/webcrypto/webcrypto_impl.h
@@ -47,6 +47,10 @@ class CONTENT_EXPORT WebCryptoImpl
       bool extractable,
       blink::WebCryptoKeyUsageMask usage_mask,
       blink::WebCryptoResult result);
+  virtual void exportKey(
+      blink::WebCryptoKeyFormat format,
+      const blink::WebCryptoKey& key,
+      blink::WebCryptoResult result);
   virtual void sign(
       const blink::WebCryptoAlgorithm& algorithm,
       const blink::WebCryptoKey& key,
@@ -105,6 +109,10 @@ class CONTENT_EXPORT WebCryptoImpl
       bool extractable,
       blink::WebCryptoKeyUsageMask usage_mask,
       blink::WebCryptoKey* key);
+  bool ExportKeyInternal(
+      blink::WebCryptoKeyFormat format,
+      const blink::WebCryptoKey& key,
+      blink::WebArrayBuffer* buffer);
   bool SignInternal(
       const blink::WebCryptoAlgorithm& algorithm,
       const blink::WebCryptoKey& key,