Simplify skiatest framework.

skiatest::Test class is now a simple struct.  Some
functionalty, such as counting errors or timing is now
handled elsewhere.

skiatest:Reporter is now a simpler abstract class.  The two
implementations handle test errors.

DM and pathops_unittest updated.

Review URL: https://codereview.chromium.org/830513004
diff --git a/tests/DataRefTest.cpp b/tests/DataRefTest.cpp
index 6a58c16..099e909 100644
--- a/tests/DataRefTest.cpp
+++ b/tests/DataRefTest.cpp
@@ -174,7 +174,7 @@
 }
 
 static void test_files(skiatest::Reporter* reporter) {
-    SkString tmpDir = skiatest::Test::GetTmpDir();
+    SkString tmpDir = skiatest::GetTmpDir();
     if (tmpDir.isEmpty()) {
         return;
     }