Add move semantics to MessageBuilder, FlatBufferBuilder, SliceAllocator, and vector_downward (#4893)

Unit tests
Update flatbuffers + gRPC build instructions
Update CMakeLists.txt with cmake variables for grpc and protobuf install paths
Update tests for travis build

CMakeLists.txt

@@ -101,6 +101,7 @@ set(FlatBuffers_GRPCTest_SRCS
   tests/monster_test.grpc.fb.h
   tests/monster_test.grpc.fb.cc
   grpc/tests/grpctest.cpp
+  grpc/tests/message_builder_test.cpp
   # file generated by running compiler on samples/monster.fbs
   ${CMAKE_CURRENT_BINARY_DIR}/samples/monster_generated.h
 )
@@ -257,6 +258,15 @@ if(FLATBUFFERS_BUILD_GRPCTEST)
   if(CMAKE_COMPILER_IS_GNUCXX)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-parameter -Wno-shadow")
   endif()
+  if(NOT GRPC_INSTALL_PATH)
+    message(SEND_ERROR "GRPC_INSTALL_PATH variable is not defined. See grpc/README.md")
+  endif()
+  if(NOT PROTOBUF_DOWNLOAD_PATH)
+    message(SEND_ERROR "PROTOBUF_DOWNLOAD_PATH variable is not defined. See grpc/README.md")
+  endif()
+  INCLUDE_DIRECTORIES(${GRPC_INSTALL_PATH}/include)
+  INCLUDE_DIRECTORIES(${PROTOBUF_DOWNLOAD_PATH}/src)
+  LINK_DIRECTORIES(${GRPC_INSTALL_PATH}/lib)
   add_executable(grpctest ${FlatBuffers_GRPCTest_SRCS})
   target_link_libraries(grpctest grpc++_unsecure grpc_unsecure gpr pthread dl)
 endif()
@@ -346,6 +356,9 @@ if(FLATBUFFERS_BUILD_TESTS)
   file(COPY "${CMAKE_CURRENT_SOURCE_DIR}/tests" DESTINATION
        "${CMAKE_CURRENT_BINARY_DIR}")
   add_test(NAME flattests COMMAND flattests)
+  if(FLATBUFFERS_BUILD_GRPCTEST)
+    add_test(NAME grpctest COMMAND grpctest)
+  endif()
 endif()
 
 include(CMake/BuildFlatBuffers.cmake)