Added DSL modifiers declarations

Change-Id: I97a7c5cfb3ce3f430074092616a3256422c8ad5e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444979
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 4a96f6e..8ba27a6 100644
--- a/tests/SkSLDSLTest.cpp
+++ b/tests/SkSLDSLTest.cpp
@@ -2130,3 +2130,10 @@
     REPORTER_ASSERT(r, DSLWriter::ProgramElements().size() == 1);
     EXPECT_EQUAL(*DSLWriter::ProgramElements()[0], "#extension test_extension : enable");
 }
+
+DEF_GPUTEST_FOR_MOCK_CONTEXT(DSLModifiersDeclaration, r, ctxInfo) {
+    AutoDSLContext context(ctxInfo.directContext()->priv().getGpu());
+    Declare(Modifiers(Layout().blendSupportAllEquations(), kOut_Modifier));
+    REPORTER_ASSERT(r, DSLWriter::ProgramElements().size() == 1);
+    EXPECT_EQUAL(*DSLWriter::ProgramElements()[0], "layout(blend_support_all_equations) out;");
+}