Adding deps to protobuf rules.

Change-Id: Ib1f4f1e061a55885389a7b51c98317ee241a1bba
diff --git a/build_tests/BUILD b/build_tests/BUILD
index be6a201..72dc6da 100644
--- a/build_tests/BUILD
+++ b/build_tests/BUILD
@@ -74,6 +74,14 @@
 proto_cc_library(
   name = 'proto_build_test_library',
   src = 'proto.proto',
+  deps = [
+    ':proto_build_test_library_base',
+  ],
+)
+
+proto_cc_library(
+  name = 'proto_build_test_library_base',
+  src = 'proto_base.proto',
 )
 
 cc_test(
diff --git a/build_tests/proto.cc b/build_tests/proto.cc
index 23ff879..bb09003 100644
--- a/build_tests/proto.cc
+++ b/build_tests/proto.cc
@@ -6,6 +6,7 @@
   ::frc971::TestProto test_proto1, test_proto2;
   test_proto1.set_s("Hi!");
   test_proto1.set_i(971);
+  test_proto1.mutable_base_proto()->set_a("silly");
 
   ::std::string serialized;
   ASSERT_TRUE(test_proto1.SerializeToString(&serialized));
diff --git a/build_tests/proto.proto b/build_tests/proto.proto
index 367a650..d0e6fe2 100644
--- a/build_tests/proto.proto
+++ b/build_tests/proto.proto
@@ -4,9 +4,13 @@
 
 import "google/protobuf/empty.proto";
 
+import "build_tests/proto_base.proto";
+
 message TestProto {
   string s = 1;
   int32 i = 2;
   // Making sure that well-known protos work.
   .google.protobuf.Empty empty = 3;
+  // Making sure we can depend on other protos.
+  BaseProto base_proto = 4;
 }
diff --git a/build_tests/proto_base.proto b/build_tests/proto_base.proto
new file mode 100644
index 0000000..8fc2143
--- /dev/null
+++ b/build_tests/proto_base.proto
@@ -0,0 +1,8 @@
+syntax = "proto2";
+
+package frc971;
+
+message BaseProto {
+  optional string a = 1;
+  optional string b = 2;
+}