Normalize _unittest.cc filename suffix for unittests

gpu/command_buffer/tests/gl_readback_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 #include <GLES2/gl2extchromium.h>
 
 #include <cmath>
 
@@ skipping 302 matching lines @@
 
     glDeleteFramebuffers(1, &framebuffer);
     glDeleteTextures(1, &texture_id);
   }
 
   glDeleteBuffers(1, &vertex_buffer);
   glDeleteProgram(program);
 }
 
 }  // namespace gpu