Increase default stack size

This increases the default stack size from 12KB to 16KB.

Bug 3388513

Change-Id: I7f7c3f75b749ca2145a96434e89e6500f79973e4
diff --git a/vm/Thread.h b/vm/Thread.h
index e805c1c..5fdb869 100644
--- a/vm/Thread.h
+++ b/vm/Thread.h
@@ -81,7 +81,7 @@
 #define kInternalRefMax         4096    /* mainly a sanity check */
 
 #define kMinStackSize       (512 + STACK_OVERFLOW_RESERVE)
-#define kDefaultStackSize   (12*1024)   /* three 4K pages */
+#define kDefaultStackSize   (16*1024)   /* four 4K pages */
 #define kMaxStackSize       (256*1024 + STACK_OVERFLOW_RESERVE)
 
 /*