Decrease number of threads in ExtensionRegistration tests for mips, current number is causing OOMs.

test/cctest/test-lockers.cc

Index: test/cctest/test-lockers.cc
===================================================================
--- test/cctest/test-lockers.cc	(revision 10046)
+++ test/cctest/test-lockers.cc	(working copy)
@@ -674,7 +674,7 @@
 // Test installing extensions in separate isolates concurrently.
 // http://code.google.com/p/v8/issues/detail?id=1821
 TEST(ExtensionsRegistration) {
-#ifdef V8_TARGET_ARCH_ARM
+#if defined V8_TARGET_ARCH_ARM || defined V8_HOST_ARCH_MIPS
   const int kNThreads = 10;
 #else
   const int kNThreads = 40;