coverage: Improve generation, see below.

runtime/vm/vm_sources.gypi

 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This file contains all sources (vm and tests) for the dart virtual machine.
 # Unit test files need to have a '_test' suffix appended to the name.
 {
   'sources': [
     'allocation.cc',
     'allocation.h',
@@ skipping 84 matching lines @@
     'compiler_test.cc',
     'constants_arm.h',
     'constants_arm64.h',
     'constants_ia32.h',
     'constants_mips.h',
     'constants_x64.h',
     'counters.cc',
     'counters.h',
     'coverage.cc',
     'coverage.h',
+    'coverage_test.cc',
     'cpu.h',
     'cpu_arm.cc',
     'cpu_arm64.cc',
     'cpu_ia32.cc',
     'cpu_mips.cc',
     'cpu_test.cc',
     'cpu_x64.cc',
     'cpuid.h',
     'cpuid.cc',
     'cpuinfo.h',
@@ skipping 310 matching lines @@
     'visitor.h',
     'vtune.cc',
     'vtune.h',
     'weak_table.cc',
     'weak_table.h',
     'zone.cc',
     'zone.h',
     'zone_test.cc',
   ],
 }