Work on Windows GN component build.

ppapi/thunk/BUILD.gn

Index: ppapi/thunk/BUILD.gn
diff --git a/ppapi/thunk/BUILD.gn b/ppapi/thunk/BUILD.gn
index 5b326e4495b96f3ba6c9a16d312bb082d3ae0d65..18096a4fbda303ae6b49c308590020e01617f4c3 100644
--- a/ppapi/thunk/BUILD.gn
+++ b/ppapi/thunk/BUILD.gn
@@ -3,6 +3,12 @@
 # found in the LICENSE file.
 
 source_set("thunk") {
+  # In GYP this is the same target as shared_impl. In GN these are split apart
+  # for clarity but to get component builds correct, targets must only depend
+  # on these via the shared_impl component.
+  # TODO(brettw) separate these when GYP compat is no longer required.
+  visibility = [ "//ppapi/shared_impl" ]
+
   sources = [
     "enter.cc",
     "enter.h",
@@ -189,5 +195,11 @@ source_set("thunk") {
     ]
   }
 
-  defines = [ "PPAPI_THUNK_IMPLEMENTATION" ]
+  defines = [
+    # This target goes in the same library as shared_impl (in GYP they are the
+    # same).
+    "PPAPI_SHARED_IMPLEMENTATION",
+
+    "PPAPI_THUNK_IMPLEMENTATION",
+  ]
 }