Set default heap size to 5MB.

Change-Id: Iac8ae3cbe6b431767776653c9f430983172cfb6f

core/java/com/android/internal/os/ZygoteInit.java

@@ -563,6 +563,8 @@ public class ZygoteInit {
 
     public static void main(String argv[]) {
         try {
+            VMRuntime.getRuntime().setMinimumHeapSize(5 * 1024 * 1024);
+
             // Start profiling the zygote initialization.
             SamplingProfilerIntegration.start();