Fix linker warning in broadcast_channel.mojom-blink.obj.

third_party/WebKit/Source/platform/weborigin/DEPS

 include_rules = [
     # net/ includes should be allowed only in a limited set of directories,
     # so we have separate DEPS from platform's one.
     "+net/base",
+
+    # weborigin sits below platform in the layer tree, so can't include headers
+    # from it. The exception is RuntimeEnabledFeatures which is its own
+    # component.
+    "-platform",
+    "-public/platform",
+    "+platform/weborigin",
+    "+platform/RuntimeEnabledFeatures.h",
 ]
+
+specific_include_rules = {
+    ".*Test\.cpp": [
+        "+platform",
+    ]
+}