Ignore libcore.java.lang.ThreadTest failures on device.

Since https://android-review.googlesource.com/#/c/209427
has been merged, libcore.java.lang.ThreadTest tests are
failing with this error on ARM64:

  java.lang.UnsatisfiedLinkError: dlopen failed: library "libnativehelper_compat_libc++.so" not found
      at java.lang.Runtime.loadLibrary0(Runtime.java:977)
      at java.lang.System.loadLibrary(System.java:1628)
      at libcore.java.lang.ThreadTest.<clinit>(ThreadTest.java:26)

Ignore those failures for now to make the build turn green
again, while we investigate.

Bug: 28082914
Change-Id: Ia8c3c776c99aace06701479d1440c828d39cbec3
diff --git a/tools/libcore_failures.txt b/tools/libcore_failures.txt
index 2533ce2..38b6ea6 100644
--- a/tools/libcore_failures.txt
+++ b/tools/libcore_failures.txt
@@ -267,6 +267,24 @@
           "libcore.util.NativeAllocationRegistryTest#testNullArguments"]
 },
 {
+  description: "libnativehelper_compat_libc++.so not found by dlopen on ARM64",
+  result: EXEC_FAILED,
+  modes: [device],
+  bug: 28082914,
+  names: ["libcore.java.lang.ThreadTest#testContextClassLoaderIsInherited",
+          "libcore.java.lang.ThreadTest#testContextClassLoaderIsNotNull",
+          "libcore.java.lang.ThreadTest#testGetAllStackTracesIncludesAllGroups",
+          "libcore.java.lang.ThreadTest#testGetStackTrace",
+          "libcore.java.lang.ThreadTest#testJavaContextClassLoader",
+          "libcore.java.lang.ThreadTest#testLeakingStartedThreads",
+          "libcore.java.lang.ThreadTest#testLeakingUnstartedThreads",
+          "libcore.java.lang.ThreadTest#testNativeThreadNames",
+          "libcore.java.lang.ThreadTest#testThreadInterrupted",
+          "libcore.java.lang.ThreadTest#testThreadSleep",
+          "libcore.java.lang.ThreadTest#testThreadSleepIllegalArguments",
+          "libcore.java.lang.ThreadTest#testThreadWakeup"]
+},
+{
   description: "Only work with --mode=activity",
   result: EXEC_FAILED,
   names: [ "libcore.java.io.FileTest#testJavaIoTmpdirMutable" ]