Fix classpath generation for Eclipse project

The GWT libraries were not included in the classpath, resulting
in the project failing to build in Eclipse.

Explicitly add the libraries as dependencies.

Bug: Issue 8792
Change-Id: I56acf2edba29f9a72eb1c489c776dad12e28614f
diff --git a/tools/eclipse/BUILD b/tools/eclipse/BUILD
index a6cc8cb..a06bb85 100644
--- a/tools/eclipse/BUILD
+++ b/tools/eclipse/BUILD
@@ -8,6 +8,8 @@
     name = "main_classpath_collect",
     testonly = 1,
     deps = GWT_PLUGIN_DEPS + [
+        "//external:gwt-dev",
+        "//external:gwt-user",
         "//:reviewers__plugin_test_deps",
     ],
 )