Only build spvtools_* when dawn_enable_spirv_validation is true

Bug: dawn:286
Change-Id: I90e641cf65cba1d480d09ad99f999c600348f887
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/172462
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
diff --git a/src/dawn/native/BUILD.gn b/src/dawn/native/BUILD.gn
index 3b750b7..6d93677 100644
--- a/src/dawn/native/BUILD.gn
+++ b/src/dawn/native/BUILD.gn
@@ -163,11 +163,6 @@
     "${dawn_root}/src/dawn/common",
     "${dawn_root}/src/tint/api",
     "${dawn_root}/src/tint/lang/wgsl/features",
-
-    # TODO(dawn:286): These should only be necessary if SPIR-V validation is
-    # enabled with dawn_enable_spirv_validation
-    "${dawn_spirv_tools_dir}:spvtools_opt",
-    "${dawn_spirv_tools_dir}:spvtools_val",
   ]
   defines = []
   libs = []
@@ -680,6 +675,10 @@
       "SpirvValidation.cpp",
       "SpirvValidation.h",
     ]
+    deps += [
+      "${dawn_spirv_tools_dir}:spvtools_opt",
+      "${dawn_spirv_tools_dir}:spvtools_val",
+    ]
   }
 
   if (dawn_enable_opengl) {