tint: Add ProgramBuilder::Else() helper

This aids readability when building chains of if-else statements.

Change-Id: I77ed5a16421bd52302db61f2776d55971838e122
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/88366
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/src/tint/writer/glsl/generator_impl_if_test.cc b/src/tint/writer/glsl/generator_impl_if_test.cc
index a5fcbc5..4b0b7bb 100644
--- a/src/tint/writer/glsl/generator_impl_if_test.cc
+++ b/src/tint/writer/glsl/generator_impl_if_test.cc
@@ -46,7 +46,7 @@
 
     auto* cond = Expr("cond");
     auto* body = Block(Return());
-    auto* i = If(cond, body, If(else_cond, else_body));
+    auto* i = If(cond, body, Else(If(else_cond, else_body)));
     WrapInFunction(i);
 
     GeneratorImpl& gen = Build();
@@ -71,7 +71,7 @@
 
     auto* cond = Expr("cond");
     auto* body = Block(Return());
-    auto* i = If(cond, body, else_body);
+    auto* i = If(cond, body, Else(else_body));
     WrapInFunction(i);
 
     GeneratorImpl& gen = Build();
@@ -99,7 +99,7 @@
 
     auto* cond = Expr("cond");
     auto* body = Block(Return());
-    auto* i = If(cond, body, If(else_cond, else_body, else_body_2));
+    auto* i = If(cond, body, Else(If(else_cond, else_body, Else(else_body_2))));
     WrapInFunction(i);
 
     GeneratorImpl& gen = Build();