Implement a basic PPAPI plugin for Blink layout tests.

content/content_shell.gypi

Index: content/content_shell.gypi
diff --git a/content/content_shell.gypi b/content/content_shell.gypi
index 07769f43ff72702078cabea827c0f3f06ae93ab9..9462cc4db937609f0b2a1e31b3cdebefc9b34d83 100644
--- a/content/content_shell.gypi
+++ b/content/content_shell.gypi
@@ -62,6 +62,7 @@
         '../media/media.gyp:media',
         '../net/net.gyp:net',
         '../net/net.gyp:net_resources',
+        '../ppapi/ppapi_internal.gyp:blink_test_plugin',
         '../skia/skia.gyp:skia',
         '../storage/storage_browser.gyp:storage',
         '../third_party/WebKit/public/blink.gyp:blink',
@@ -735,6 +736,14 @@
           ],
           'copies': [
             {
+              # PPAPI test plugins are loaded relative to DIR_MODULE. On OS X,
+              # that corresponds to Content Shell Framework.framework.
+              'destination': '<(PRODUCT_DIR)/$(CONTENTS_FOLDER_PATH)',
+              'files': [
+                '<(PRODUCT_DIR)/blink_test_plugin.plugin',
+              ],
+            },
+            {
               'destination': '<(PRODUCT_DIR)/$(CONTENTS_FOLDER_PATH)/Resources',
               'files': [
                 '<(PRODUCT_DIR)/crash_inspector',