[Android] Make SetJavaAsserts return True if a restart is required.

BUG=417705

Review URL: https://codereview.chromium.org/602973004

Cr-Commit-Position: refs/heads/master@{#296736}

build/android/pylib/device/device_utils.py

@@ -689,10 +689,14 @@ class DeviceUtils(object):
       timeout: timeout in seconds
       retries: number of retries
 
+    Returns:
+      True if the device-side property changed and a restart is required as a
+      result, False otherwise.
+
     Raises:
       CommandTimeoutError on timeout.
     """
-    self.old_interface.SetJavaAssertsEnabled(enabled)
+    return self.old_interface.SetJavaAssertsEnabled(enabled)
 
   @decorators.WithTimeoutAndRetriesFromInstance()
   def GetProp(self, property_name, timeout=None, retries=None):

build/android/pylib/device/device_utils_test.py

@@ -1312,7 +1312,7 @@ class DeviceUtilsSetJavaAssertsTest(DeviceUtilsOldImplTest):
            ('adb -s 0123456789abcdef shell '
                 'setprop dalvik.vm.enableassertions "all"',
             '')]):
-        self.device.SetJavaAsserts(True)
+        self.assertTrue(self.device.SetJavaAsserts(True))
 
   def testSetJavaAsserts_disable(self):
     mock_file = self.mockNamedTemporary(
@@ -1336,7 +1336,7 @@ class DeviceUtilsSetJavaAssertsTest(DeviceUtilsOldImplTest):
            ('adb -s 0123456789abcdef shell '
                 'setprop dalvik.vm.enableassertions ""',
             '')]):
-        self.device.SetJavaAsserts(False)
+        self.assertTrue(self.device.SetJavaAsserts(False))
 
   def testSetJavaAsserts_alreadyEnabled(self):
     mock_file = self.mockNamedTemporary(