Protect AudioRendererAlgorithm from invalid step sizes.

BUG=165430
TEST=unittests and asan pass.

Review URL: https://codereview.chromium.org/11573023

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@173249 0039d316-1c4b-4281-b951-d872f2087c98
  void WriteFakeData(uint8* audio_data, size_t length) {

  void WriteFakeData(uint8* audio_data, size_t length) {
    Type* output = reinterpret_cast<Type*>(audio_data);
    for (size_t i = 0; i < length; i++) {
      output[i] = i % 5 + 10;
    }
  }
