Fix HLSL emission of cbuffers

Despite the documentation claiming otherwise, the DXC doesn't allow
these to be anonymous.

Change-Id: I853d11970890106b8fd4d6b8bb321940f0658bd3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35281
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/writer/hlsl/generator_impl.cc

diff --git a/src/writer/hlsl/generator_impl.cc b/src/writer/hlsl/generator_impl.cc
index 03d86ce..b480acf 100644
--- a/src/writer/hlsl/generator_impl.cc
+++ b/src/writer/hlsl/generator_impl.cc
@@ -1334,7 +1334,9 @@
       // is not a block.
       // Relevant: https://github.com/gpuweb/gpuweb/issues/1004
       //           https://github.com/gpuweb/gpuweb/issues/1008
-      out << "cbuffer : register(b" << binding->value() << ") {" << std::endl;
+      auto name = "cbuffer_" + var->name();
+      out << "cbuffer " << name << " : register(b" << binding->value() << ") {"
+          << std::endl;
 
       increment_indent();
       make_indent(out);

src/writer/hlsl/generator_impl_function_test.cc

diff --git a/src/writer/hlsl/generator_impl_function_test.cc b/src/writer/hlsl/generator_impl_function_test.cc
index cc35e8a..a20f2f4 100644
--- a/src/writer/hlsl/generator_impl_function_test.cc
+++ b/src/writer/hlsl/generator_impl_function_test.cc
@@ -268,7 +268,7 @@
 
   ASSERT_TRUE(td.Determine()) << td.error();
   ASSERT_TRUE(gen.Generate(out)) << gen.error();
-  EXPECT_EQ(result(), R"(cbuffer : register(b0) {
+  EXPECT_EQ(result(), R"(cbuffer cbuffer_coord : register(b0) {
   float4 coord;
 };
 
@@ -819,7 +819,7 @@
 
   ASSERT_TRUE(td.Determine()) << td.error();
   ASSERT_TRUE(gen.Generate(out)) << gen.error();
-  EXPECT_EQ(result(), R"(cbuffer : register(b0) {
+  EXPECT_EQ(result(), R"(cbuffer cbuffer_coord : register(b0) {
   float4 coord;
 };