Remove dependency on //crypto in //ipc, except on windows.

ipc/brokerable_attachment.h

Index: ipc/brokerable_attachment.h
diff --git a/ipc/brokerable_attachment.h b/ipc/brokerable_attachment.h
index 9c2bbbd69ec444ac0770a1df93cf7ae34110be20..36e8b3a651d1e420c5b0174d3d766c2f830835fa 100644
--- a/ipc/brokerable_attachment.h
+++ b/ipc/brokerable_attachment.h
@@ -22,15 +22,6 @@ class IPC_EXPORT BrokerableAttachment : public MessageAttachment {
   struct IPC_EXPORT AttachmentId {
     uint8_t nonce[kNonceSize];
 
-    // Default constructor returns an unguessable random nonce.
-    AttachmentId();
-
-    // Constructs an AttachmentId from a buffer.
-    AttachmentId(const char* start_address, size_t size);
-
-    // Writes the nonce into a buffer.
-    void SerializeToBuffer(char* start_address, size_t size);
-
     bool operator==(const AttachmentId& rhs) const {
       for (size_t i = 0; i < kNonceSize; ++i) {
         if (nonce[i] != rhs.nonce[i])
@@ -73,7 +64,6 @@ class IPC_EXPORT BrokerableAttachment : public MessageAttachment {
   virtual BrokerableType GetBrokerableType() const = 0;
 
  protected:
-  BrokerableAttachment();
   BrokerableAttachment(const AttachmentId& id, bool needs_brokering);
   ~BrokerableAttachment() override;