Make it possible to enable tlab with a build parameter.

For testing.

Change-Id: I4d06a4db733b7fa09105f068028483cf88db7925
diff --git a/build/Android.common_build.mk b/build/Android.common_build.mk
index 08b4ec2..8f00298 100644
--- a/build/Android.common_build.mk
+++ b/build/Android.common_build.mk
@@ -219,6 +219,10 @@
   art_cflags += -DART_USE_READ_BARRIER=1
 endif
 
+ifeq ($(ART_USE_TLAB),true)
+  art_cflags += -DART_USE_TLAB=1
+endif
+
 # Cflags for non-debug ART and ART tools.
 art_non_debug_cflags := \
   -O3