Add KeyBlob ctor that takes pointer to key material.

This is used by a vendor-specific implementation and was removed
in the KeyBlob refactor.

Change-Id: I98c33d389844c592d8325c6184ec071106622c14
diff --git a/key_blob.cpp b/key_blob.cpp
index 188e759..6b24355 100644
--- a/key_blob.cpp
+++ b/key_blob.cpp
@@ -24,10 +24,13 @@
 const size_t KeyBlob::NONCE_LENGTH;
 const size_t KeyBlob::TAG_LENGTH;
 
+KeyBlob::KeyBlob(const uint8_t* key_blob, size_t key_blob_length) : error_(KM_ERROR_OK) {
+    Deserialize(&key_blob, key_blob + key_blob_length);
+}
+
 KeyBlob::KeyBlob(const keymaster_key_blob_t& key_blob) : error_(KM_ERROR_OK) {
     const uint8_t* key_material = key_blob.key_material;
-    if (!Deserialize(&key_material, key_blob.key_material + key_blob.key_material_size))
-        return;
+    Deserialize(&key_material, key_blob.key_material + key_blob.key_material_size);
 }
 
 size_t KeyBlob::SerializedSize() const {