ART: Use core image to speed up some gtests.

Host timing of
  art_compiler_tests --no_isolate --gtest_filter='<pattern>'
for different patterns:
  "ms total"                    before after
  LoadStoreEliminationTest*      16945  4750
  LoadStoreAnalysisTest*          2647   689
  ReferenceTypePropagationTest*  13542  3929
  InstructionSimplifierTest*      1452   406

Host timing of
  art_runtime_tests --no_isolate --gtest_filter='<pattern>'
for different patterns:
  "ms total"                    before after
  RegType*Test*                   2976  1675
  DexCacheTest*                    265    74
  JavaVmExtTest*                   785   230

Host timing of
  art_libartbase_tests --no_isolate --gtest_filter='<pattern>'
for different patterns:
  "ms total"                    before after
  FlagsTests*                      691   214

Host timing of
  art_dex2oat_tests --no_isolate --gtest_filter='<pattern>'
for different patterns:
  "ms total"                    before after
  VerifierDepsTest*               3567   874

Test: m test-art-host-gtest
Change-Id: I20df90e3d38aaa286e22ba070c7845bcb09e3bca
diff --git a/runtime/common_runtime_test.h b/runtime/common_runtime_test.h
index 7c11fd8..9fa9c5d 100644
--- a/runtime/common_runtime_test.h
+++ b/runtime/common_runtime_test.h
@@ -207,6 +207,8 @@
 
   std::unique_ptr<CompilerCallbacks> callbacks_;
 
+  bool use_boot_image_;
+
   virtual void SetUp();
 
   virtual void TearDown();