Split apart the PPAPI GN targets

ppapi/cpp/BUILD.gn

+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//ppapi/ppapi_sources.gni")
+
+# Link to this target to get the PPAPI C++ wrapper objects and plugin startup
+# code. See also "objects" below.
+source_set("cpp") {
+  sources = [
+    "module_embedder.h",
+    "ppp_entrypoints.cc",
+  ]
+
+  deps = [
+    ":objects",
+    "//ppapi/c",
+  ]
+}
+
+# Link to this target to get only the PPAPI C++ wrapper objects but not the
+# plugin startup code. Some plugins need special startup code that they supply
+# themselves.
+source_set("objects") {
+  sources = rebase_path(ppapi_sources.cpp_source_files, ".", "..")
+}