Turn on dexmaker sharing classloaders for sysui tests

This will allow us to mock package private things. It also happens
to speed up the tests, a lot.

Test: runtest systemui
Change-Id: I48f39ee282a4ea3163c642c8290f302428c4a5f4

packages/SystemUI/tests/src/com/android/systemui/SysuiTestCase.java

@@ -37,6 +37,7 @@ public abstract class SysuiTestCase {
 
     @Before
     public void SysuiSetup() throws Exception {
+        System.setProperty("dexmaker.share_classloader", "true");
         mContext = new TestableContext(InstrumentationRegistry.getTargetContext(), this);
     }