Start adding implementations for runtime-provided native methods.

The library can't do everything...

Change-Id: Ib808c00570c7214aeb2ca058b1a66cacbeb372f1
diff --git a/src/heap.h b/src/heap.h
index d4d43e7..72ceffa 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -44,6 +44,13 @@
   // Initiates an explicit garbage collection.
   static void CollectGarbage();
 
+  // Implements java.lang.Runtime.maxMemory.
+  static int64_t GetMaxMemory();
+  // Implements java.lang.Runtime.totalMemory.
+  static int64_t GetTotalMemory();
+  // Implements java.lang.Runtime.freeMemory.
+  static int64_t GetFreeMemory();
+
   // Blocks the caller until the garbage collector becomes idle.
   static void WaitForConcurrentGcToComplete();