[spirv-writer] Output name for constant global variables.

When emitting a global constant we'd early exit the emission code before
emitting the debug statement for the constants name. This Cl adds the
needed code to emit names for global constants.

Change-Id: I1a7a3660b4ff31879393a6a776a9f00e895de216
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/26923
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>

src/writer/spirv/builder.cc

@@ -556,6 +556,9 @@ bool Builder::GenerateGlobalVariable(ast::Variable* var) {
       error_ = "missing constructor for constant";
       return false;
     }
+    push_debug(spv::Op::OpName,
+               {Operand::Int(init_id), Operand::String(var->name())});
+
     scope_stack_.set_global(var->name(), init_id);
     spirv_id_to_variable_[init_id] = var;
     return true;

src/writer/spirv/builder_global_variable_test.cc

@@ -157,6 +157,8 @@ TEST_F(BuilderTest, GlobalVar_Const) {
   EXPECT_TRUE(b.GenerateGlobalVariable(&v)) << b.error();
   ASSERT_FALSE(b.has_error()) << b.error();
 
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %5 "var"
+)");
   EXPECT_EQ(DumpInstructions(b.types()), R"(%2 = OpTypeFloat 32
 %1 = OpTypeVector %2 3
 %3 = OpConstant %2 1