tools: implement blob read

Implement blob read.  This isn't currently used by the flash update
process however, it is useful.

Tested: Verified it read back bytes written to another blob handler.
Change-Id: Ib1590448d0bfaa3d4fde20ae8bae353c9107e5c4
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/blob_interface_mock.hpp b/test/blob_interface_mock.hpp
index 520d5b4..845d7c1 100644
--- a/test/blob_interface_mock.hpp
+++ b/test/blob_interface_mock.hpp
@@ -19,6 +19,9 @@
                  std::uint16_t(const std::string&,
                                blobs::FirmwareBlobHandler::UpdateFlags));
     MOCK_METHOD1(closeBlob, void(std::uint16_t));
+    MOCK_METHOD3(readBytes,
+                 std::vector<std::uint8_t>(std::uint16_t, std::uint32_t,
+                                           std::uint32_t));
 };
 
 } // namespace host_tool