Update ART tests to handle new System.gc behavior

Changed calls from System.gc to Runtime.getRuntime.gc where it was
necessary.

Required for:
https://android-review.googlesource.com/#/c/80253/

Change-Id: I2b0622585da54229a6248e95d40134b6d18598a9
diff --git a/test/079-phantom/src/Main.java b/test/079-phantom/src/Main.java
index 9c459c9..c54bc0b 100644
--- a/test/079-phantom/src/Main.java
+++ b/test/079-phantom/src/Main.java
@@ -38,29 +38,29 @@
     public void run() {
         createBitmaps();
 
-        System.gc();
+        Runtime.getRuntime().gc();
         sleep(250);
 
         mBitmap2.drawAt(0, 0);
 
         System.out.println("nulling 1");
         mBitmap1 = null;
-        System.gc();
+        Runtime.getRuntime().gc();
         sleep(500);
 
         System.out.println("nulling 2");
         mBitmap2 = null;
-        System.gc();
+        Runtime.getRuntime().gc();
         sleep(500);
 
         System.out.println("nulling 3");
         mBitmap3 = null;
-        System.gc();
+        Runtime.getRuntime().gc();
         sleep(500);
 
         System.out.println("nulling 4");
         mBitmap4 = null;
-        System.gc();
+        Runtime.getRuntime().gc();
         sleep(500);
 
         Bitmap.shutDown();