Change MemMap::maps_ to not be global variable

Runtime.exit() was causing globals to get destructed at the same time
that another thread was using it for allocating a new mem map.

Bug: 17962201
Change-Id: I400cb7b8141d858f3c08a6fe59a02838c04c6962
diff --git a/compiler/common_compiler_test.cc b/compiler/common_compiler_test.cc
index e3eb9e9..d1d47fb 100644
--- a/compiler/common_compiler_test.cc
+++ b/compiler/common_compiler_test.cc
@@ -397,6 +397,7 @@
   // Reserve where the image will be loaded up front so that other parts of test set up don't
   // accidentally end up colliding with the fixed memory address when we need to load the image.
   std::string error_msg;
+  MemMap::Init();
   image_reservation_.reset(MemMap::MapAnonymous("image reservation",
                                                 reinterpret_cast<uint8_t*>(ART_BASE_ADDRESS),
                                                 (size_t)100 * 1024 * 1024,  // 100MB