Add usage of main from chromium when part of a chromium build

BUG=tint:123

Change-Id: Ic7a8694cefd0dbee2a1855e84f4ffaaf75ad6e7a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25520
Reviewed-by: Ryan Harrison <rharrison@chromium.org>

BUILD.gn

@@ -638,6 +638,20 @@ if (!build_with_chromium) {
   }
 }
 
+###############################################################################
+# Wrapping of Chromium targets
+###############################################################################
+# These targets are separated because they are Chromium sources files that
+# can't use the tint_internal config, otherwise Tint's warning flags get
+# applied while compiling a bunch of Chromium's //base (via header inclusion)
+if (build_with_chromium) {
+  source_set("tint_unittests_main") {
+    testonly = true
+    deps = [ ":gmock_and_gtest" ]
+    sources = [ "//gpu/tint_unittests_main.cc" ]
+  }
+}
+
 ###############################################################################
 # Tests - For libtint core and optional modules
 ###############################################################################
@@ -1089,8 +1103,9 @@ test("tint_unittests") {
     "${tint_spirv_tools_dir}/:spvtools_val",
   ]
 
-  # TODO(rharrison): Use main() from chromium for chromium tree builds. This
-  # requires adding a file to //gpu like Dawn has done.
+  if (build_with_chromium) {
+    deps += [ ":tint_unittests_main" ]
+  }
 
   configs += [
     ":tint_common_config",