Add unit test for control statements in do-while loop.

Change-Id: I8309940f8e40d0e84847ae272830896d010c39de
Bug: skia:11219
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/359138
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

gn/sksl_tests.gni

@@ -302,6 +302,7 @@ sksl_shared_tests = [
   "/sksl/shared/DependentInitializers.sksl",
   "/sksl/shared/DerivativesUnused.sksl",
   "/sksl/shared/Discard.sksl",
+  "/sksl/shared/DoWhileControlFlow.sksl",
   "/sksl/shared/Enum.sksl",
   "/sksl/shared/FragCoordsFlipY.sksl",
   "/sksl/shared/FragCoordsNew.sksl",

resources/sksl/shared/DoWhileControlFlow.sksl

@@ -0,0 +1,19 @@
+half4 main() {
+    half4 x = half4(1, 1, 1, 1);
+
+    // Verify that break is allowed in a do-while loop.
+    do {
+        x.r -= 0.25;
+        if (x.r <= 0) break;
+    } while (x.a == 1);
+
+    // Verify that continue is allowed in a do-while loop.
+    do {
+        x.b -= 0.25;
+        if (x.a == 1) continue; // should always happen
+        x.g = 0;
+    } while (x.b > 0);
+
+    // x contains green.
+    return x;
+}

tests/sksl/shared/DoWhileControlFlow.asm.frag

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 7: break statement must be inside a loop or switch
+1 error

tests/sksl/shared/DoWhileControlFlow.glsl

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 7: break statement must be inside a loop or switch
+1 error

tests/sksl/shared/DoWhileControlFlow.metal

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 7: break statement must be inside a loop or switch
+1 error