Added DSL extension support

Change-Id: Ia6dd32e91aa242162d4687f5c05832b87e2560ca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444977
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
diff --git a/tests/SkSLDSLTest.cpp b/tests/SkSLDSLTest.cpp
index ce9ec59..4a96f6e 100644
--- a/tests/SkSLDSLTest.cpp
+++ b/tests/SkSLDSLTest.cpp
@@ -2123,3 +2123,10 @@
             "}");
     }
 }
+
+DEF_GPUTEST_FOR_MOCK_CONTEXT(DSLExtension, r, ctxInfo) {
+    AutoDSLContext context(ctxInfo.directContext()->priv().getGpu());
+    AddExtension("test_extension");
+    REPORTER_ASSERT(r, DSLWriter::ProgramElements().size() == 1);
+    EXPECT_EQUAL(*DSLWriter::ProgramElements()[0], "#extension test_extension : enable");
+}