Metal: Restrict test shader link to 10.14+

The embedded metallib uses MTLLanguageVersion2_1, available only
macOS 10.14+.

Bug: 1046671
Change-Id: Iac72569f4d9ad25ced7c0284dbbfd790ab3ecd4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2028266Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736512}

components/metal_util/test_shader.mm

@@ -656,7 +656,7 @@ class API_AVAILABLE(macos(10.11)) TestShaderState
 void TestRenderPipelineStateNow(base::scoped_nsprotocol<id<MTLDevice>> device,
                                 const base::TimeDelta& timeout,
                                 TestShaderCallback callback)
-    API_AVAILABLE(macos(10.11)) {
+    API_AVAILABLE(macos(10.14)) {
   // Load the library binary. This should not fail.
   base::ScopedDispatchObject<dispatch_data_t> library_data = GetLibraryData();
   NSError* error = nil;
@@ -763,12 +763,17 @@ void TestShader(TestShaderCallback callback,
                                    std::move(callback));
           break;
         case TestShaderComponent::kLink:
-          closure = base::BindOnce(&TestRenderPipelineStateNow, device, timeout,
-                                   std::move(callback));
+          // The metallib listed above is in MTLLanguageVersion2_1, which is
+          // available only on 10.14 and above.
+          if (@available(macOS 10.14, *)) {
+            closure = base::BindOnce(&TestRenderPipelineStateNow, device,
+                                     timeout, std::move(callback));
+          }
           break;
       }
 
       // Run either immediately or after the specified delay.
+      if (closure) {
         if (delay.is_zero()) {
           std::move(closure).Run();
         } else {
@@ -780,6 +785,7 @@ void TestShader(TestShaderCallback callback,
         return;
       }
     }
+  }
   std::move(callback).Run(TestShaderResult::kNotAttempted, base::TimeDelta(),
                           base::TimeDelta());
 }