Add third party Rust dependency on base64.

We seem to have picked this up as a transitive dependency already
and so this is a bit simpler than it would otherwise be.

Change-Id: Ib248757b922ccf69135abe9dfc76feb120beaed0
diff --git a/rustc_deps/Cargo.lock b/rustc_deps/Cargo.lock
index 93ca992..d6cf877 100644
--- a/rustc_deps/Cargo.lock
+++ b/rustc_deps/Cargo.lock
@@ -229,6 +229,7 @@
 name = "fuchsia-third-party"
 version = "0.1.0"
 dependencies = [
+ "base64 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitfield 0.12.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/rustc_deps/Cargo.toml b/rustc_deps/Cargo.toml
index 75a7276..1cf374b 100644
--- a/rustc_deps/Cargo.toml
+++ b/rustc_deps/Cargo.toml
@@ -8,6 +8,7 @@
 authors = ["cramertj <cramertj@google.com>"]
 
 [dependencies]
+base64 = "0.8.0"
 bincode = "1"
 bitfield = "0.12"
 bitflags = "1"