Added benchmark test for rosidl_generator_c

[ahcorde]

This PR builds on top of these other PRs

• Add benchmarks for rosidl_runtime_* packages #521
• Added benchmark to rosidl_runtime_cpp bounded vector #528

Addes some performance test to the interfaces init() and destroy() functions.

Signed-off-by: ahcorde ahcorde@gmail.com

[cottsay]

I don't understand why the tests are exercising array assignments. We're not really expecting C operations like arr->bool_values[i] = true; to change in performance, and it doesn't result in any lines of code in rosidl_generator_c being exercised, so I don't see any reason to track it here. rosidl_runtime_c__String__assign is already tracked by another test, so I don't see any reason to measure that performance either.

After looking at the generated code output from this package, I really only see allocation and de-allocation functions that could be worth testing. Am I missing something?

[cottsay]

Rather than this, enable the language only if BUILD_TESTING is specified as is done here:

rosidl/rosidl_runtime_c/CMakeLists.txt

Lines 56 to 61 in 99e05f8

	# For gtest
	enable_language(CXX)
	# Default to C++14
	if(NOT CMAKE_CXX_STANDARD)
	set(CMAKE_CXX_STANDARD 14)
	endif()

Suggested change

	project(rosidl_generator_c C CXX)
	project(rosidl_generator_c C)