Fix oat_test

by reducing the DexFileCount test condition from static to dynamically
determined.

Change-Id: I3d97009a1ebfbe3ac9d41f0cdd508db0155660f8
diff --git a/compiler/oat_test.cc b/compiler/oat_test.cc
index 0747756..618aab0 100644
--- a/compiler/oat_test.cc
+++ b/compiler/oat_test.cc
@@ -127,7 +127,7 @@
   ASSERT_TRUE(oat_file.get() != nullptr) << error_msg;
   const OatHeader& oat_header = oat_file->GetOatHeader();
   ASSERT_TRUE(oat_header.IsValid());
-  ASSERT_EQ(1U, oat_header.GetDexFileCount());  // core
+  ASSERT_EQ(class_linker->GetBootClassPath().size(), oat_header.GetDexFileCount());  // core
   ASSERT_EQ(42U, oat_header.GetImageFileLocationOatChecksum());
   ASSERT_EQ(4096U, oat_header.GetImageFileLocationOatDataBegin());
   ASSERT_EQ("lue.art", std::string(oat_header.GetStoreValueByKey(OatHeader::kImageLocationKey)));