Add UI_DEVTOOLS_EXPORT so tests can mock FrontendChannel

components/ui_devtools/inspector_protocol_config.json

Index: components/ui_devtools/inspector_protocol_config.json
diff --git a/components/ui_devtools/inspector_protocol_config.json b/components/ui_devtools/inspector_protocol_config.json
index 81d216cd6c9a1494fb162ccb3ab1a7754cda94f2..83a5e6611543c1f72df9ccfa2c9fd5bf3f989994 100644
--- a/components/ui_devtools/inspector_protocol_config.json
+++ b/components/ui_devtools/inspector_protocol_config.json
@@ -3,12 +3,16 @@
         "path": "protocol.json",
         "package": "components/ui_devtools",
         "output": "",
-        "namespace": ["ui", "devtools", "protocol"]
+        "namespace": ["ui", "devtools", "protocol"],
+        "export_macro": "UI_DEVTOOLS_EXPORT",
+        "export_header": "components/ui_devtools/devtools_export.h"
     },
     "lib": {
         "package": "components/ui_devtools",
         "output": "",
         "string_header": "components/ui_devtools/string_util.h",
-        "platform_header": "components/ui_devtools/protocol_platform.h"
+        "platform_header": "components/ui_devtools/protocol_platform.h",
+        "export_macro": "UI_DEVTOOLS_EXPORT",
+        "export_header": "components/ui_devtools/devtools_export.h"
     }
 }