Add GS Invocations caps to SkSL StandaloneShaderCaps

Bug: skia:
Change-Id: I58f0caf97048e62a11cf8732acc79e3c2fbc683b
Reviewed-on: https://skia-review.googlesource.com/56801
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/SkSLUtil.h b/src/sksl/SkSLUtil.h
index c4a6475..a8be7ef 100644
--- a/src/sksl/SkSLUtil.h
+++ b/src/sksl/SkSLUtil.h
@@ -155,12 +155,16 @@
         return nullptr;
     }
 
+    const char* gsInvocationsExtensionString() const {
+        return nullptr;
+    }
+
     const char* versionDeclString() const {
         return "";
     }
 
-    bool mustImplementGSInvocationsWithLoop() const {
-        return false;
+    bool gsInvocationsSupport() const {
+        return true;
     }
 
     bool canUseFractForNegativeValues() const {