Implement GetSystemLog on Linux platform

telemetry/telemetry/core/platform_unittest.py

Index: telemetry/telemetry/core/platform_unittest.py
diff --git a/telemetry/telemetry/core/platform_unittest.py b/telemetry/telemetry/core/platform_unittest.py
index 5a838d2f9b171b178bb22ee1266fe334108ba7c5..08d6271cbd8f97b0c0dc30b1ae1ab0a211e413b4 100644
--- a/telemetry/telemetry/core/platform_unittest.py
+++ b/telemetry/telemetry/core/platform_unittest.py
@@ -43,3 +43,8 @@ class PlatformScreenshotTest(tab_test_case.TabTestCase):
       self.assertTrue(special_colored_pixel in screenshot_pixels)
     finally:
       os.remove(tf.name)
+
+  # GetSystemLog still need to be implemented on Android & Win platform.
+  @decorators.Disabled('android', 'win')

[Ken Russell (switch to Gerrit), 2017/05/07 18:56:49]

Is this Disabled attribute sufficient? It looks like GetSystemLog is implemented
only on macOS and Linux (with this CL). What about ChromeOS, for example?

Perhaps explicitly enable this test on the platforms where it's known to pass?

+  def testSmokeSystemLog(self):
+    self.assertIsNotNone(self._platform.GetSystemLog())