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..51a2190783f8ffb7062f0be580d3ceb4ad4a6e6e 100644
--- a/ppapi/thunk/BUILD.gn
+++ b/ppapi/thunk/BUILD.gn
@@ -3,6 +3,11 @@
 # found in the LICENSE file.
 
 source_set("thunk") {
+  # In GYP this is the same target as shared_impl. In GN these are split apart
+  # but to get component builds correct, targets must only depend on these
+  # via the shared_impl component.

[Dirk Pranke, 2015/04/06 16:54:07]

what's the advantage to having this be a separate source_set if only one target
can include it? Do you need to keep it separate so that you can set
PPAPI_SHARED_IMPLEMENTATION on just these files?

+  visibility = [ "//ppapi/shared_impl" ]
+
   sources = [
     "enter.cc",
     "enter.h",
@@ -189,5 +194,11 @@ 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",
+  ]
 }