Oat file checksums for boot image extensions.

Modify the oat checksums check for boot image extensions.
There may be more extensions loaded at runtime than when the
oat file was compiled, so we need to check the checksum type
from the checksums string to determine whether to use an
image checksum or dex file checksum. Different checksums
can be valid for the same boot class path.

The creation of boot image extensions and other aspects
of loading them shall be implemented in separate CLs.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: aosp_taimen-userdebug boots.
Change-Id: I43d1f9464678784e902ad72f4a89cf38b4786122
diff --git a/runtime/oat_file_assistant.h b/runtime/oat_file_assistant.h
index 1f3f74f..b5812f9 100644
--- a/runtime/oat_file_assistant.h
+++ b/runtime/oat_file_assistant.h
@@ -439,7 +439,7 @@
   // File descriptor corresponding to apk, dex file, or zip.
   int zip_fd_;
 
-  size_t cached_boot_class_path_checksum_component_count_ = 0u;
+  std::string cached_boot_class_path_;
   std::string cached_boot_class_path_checksums_;
 
   friend class OatFileAssistantTest;