Move adbd's legacy USB implementation to fastboot.

This code path is effectively dead in adbd, and fastboot's dependency on
libadbd makes it hard to refactor adbd's dependencies.

Bug: http://b/150317254
Test: built and flashed aosp_walleye-eng
Change-Id: I5118136d32fdcbbd011559ed0a4a71e1dc7bf064
diff --git a/adb/transport.h b/adb/transport.h
index 3a77cf6..b1984db 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -39,7 +39,6 @@
 #include "adb.h"
 #include "adb_unique_fd.h"
 #include "types.h"
-#include "usb.h"
 
 typedef std::unordered_set<std::string> FeatureSet;
 
@@ -204,20 +203,6 @@
     std::unique_ptr<adb::tls::TlsConnection> tls_;
 };
 
-struct UsbConnection : public BlockingConnection {
-    explicit UsbConnection(usb_handle* handle) : handle_(handle) {}
-    ~UsbConnection();
-
-    bool Read(apacket* packet) override final;
-    bool Write(apacket* packet) override final;
-    bool DoTlsHandshake(RSA* key, std::string* auth_key) override final;
-
-    void Close() override final;
-    virtual void Reset() override final;
-
-    usb_handle* handle_;
-};
-
 // Waits for a transport's connection to be not pending. This is a separate
 // object so that the transport can be destroyed and another thread can be
 // notified of it in a race-free way.
@@ -253,6 +238,10 @@
     Abort,
 };
 
+#if ADB_HOST
+struct usb_handle;
+#endif
+
 class atransport : public enable_weak_from_this<atransport> {
   public:
     // TODO(danalbert): We expose waaaaaaay too much stuff because this was
@@ -293,8 +282,10 @@
         return connection_;
     }
 
+#if ADB_HOST
     void SetUsbHandle(usb_handle* h) { usb_handle_ = h; }
     usb_handle* GetUsbHandle() { return usb_handle_; }
+#endif
 
     const TransportId id;
 
@@ -401,8 +392,10 @@
     // The underlying connection object.
     std::shared_ptr<Connection> connection_ GUARDED_BY(mutex_);
 
+#if ADB_HOST
     // USB handle for the connection, if available.
     usb_handle* usb_handle_ = nullptr;
+#endif
 
     // A callback that will be invoked when the atransport needs to reconnect.
     ReconnectCallback reconnect_;
@@ -443,8 +436,15 @@
 #endif
 
 void register_transport(atransport* transport);
-void register_usb_transport(usb_handle* h, const char* serial,
-                            const char* devpath, unsigned writeable);
+
+#if ADB_HOST
+void init_usb_transport(atransport* t, usb_handle* usb);
+void register_usb_transport(usb_handle* h, const char* serial, const char* devpath,
+                            unsigned writeable);
+
+// This should only be used for transports with connection_state == kCsNoPerm.
+void unregister_usb_transport(usb_handle* usb);
+#endif
 
 /* Connect to a network address and register it as a device */
 void connect_device(const std::string& address, std::string* response);
@@ -454,9 +454,6 @@
                                atransport::ReconnectCallback reconnect, bool use_tls,
                                int* error = nullptr);
 
-// This should only be used for transports with connection_state == kCsNoPerm.
-void unregister_usb_transport(usb_handle* usb);
-
 bool check_header(apacket* p, atransport* t);
 
 void close_usb_devices(bool reset = false);