ART: Store classpath information into oat file

Store a "dependency list" of class-path dex-files into the key-value
store of an oat file. The list is made up of dex locations and
corresponding checksums.

Add tests for encoding, decoding and checking the list.

Bug: 19781184
Change-Id: Ie700dd37e6e086db599c95d329ac1f1d2ff0b758
diff --git a/runtime/oat.h b/runtime/oat.h
index de95fef..a31e09a 100644
--- a/runtime/oat.h
+++ b/runtime/oat.h
@@ -38,6 +38,7 @@
   static constexpr const char* kDex2OatCmdLineKey = "dex2oat-cmdline";
   static constexpr const char* kDex2OatHostKey = "dex2oat-host";
   static constexpr const char* kPicKey = "pic";
+  static constexpr const char* kClassPathKey = "classpath";
 
   static OatHeader* Create(InstructionSet instruction_set,
                            const InstructionSetFeatures* instruction_set_features,