Add plugins::TestPluginPlaceholder class and allow its use in Blink layout tests.

content/content_shell.gypi

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'content_shell_product_name': 'Content Shell',
     # The "19" is so that sites that sniff for version think that this is
     # something reasonably current; the "77.34.5" is a hint that this isn't a
     # standard Chrome.
@@ skipping 32 matching lines @@
         'layouttest_support_content',
         '../base/base.gyp:base',
         '../base/base.gyp:base_static',
         '../base/third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',
         '../cc/blink/cc_blink.gyp:cc_blink',
         '../cc/cc.gyp:cc',
         '../components/components.gyp:crash_component_breakpad_mac_to_be_deleted',
         '../components/components.gyp:devtools_discovery',
         '../components/components.gyp:devtools_http_handler',
         '../components/components.gyp:web_cache_renderer',
+        '../components/components.gyp:plugins_renderer',
         '../device/bluetooth/bluetooth.gyp:device_bluetooth',
         '../device/bluetooth/bluetooth.gyp:device_bluetooth_mocks',
         '../gin/gin.gyp:gin',
         '../gpu/gpu.gyp:gpu',
         '../ipc/ipc.gyp:ipc',
         '../media/blink/media_blink.gyp:media_blink',
         '../media/media.gyp:media',
         '../net/net.gyp:net',
         '../net/net.gyp:net_resources',
         '../skia/skia.gyp:skia',
@@ skipping 208 matching lines @@
         'shell/renderer/test_runner/mock_webrtc_peer_connection_handler.cc',
         'shell/renderer/test_runner/mock_webrtc_peer_connection_handler.h',
         'shell/renderer/test_runner/spell_check_client.cc',
         'shell/renderer/test_runner/spell_check_client.h',
         'shell/renderer/test_runner/test_common.cc',
         'shell/renderer/test_runner/test_common.h',
         'shell/renderer/test_runner/test_interfaces.cc',
         'shell/renderer/test_runner/test_interfaces.h',
         'shell/renderer/test_runner/test_plugin.cc',
         'shell/renderer/test_runner/test_plugin.h',
+        'shell/renderer/test_runner/test_plugin_placeholder.cc',
+        'shell/renderer/test_runner/test_plugin_placeholder.h',
         'shell/renderer/test_runner/test_runner.cc',
         'shell/renderer/test_runner/test_runner.h',
         'shell/renderer/test_runner/text_input_controller.cc',
         'shell/renderer/test_runner/text_input_controller.h',
         'shell/renderer/test_runner/web_ax_object_proxy.cc',
         'shell/renderer/test_runner/web_ax_object_proxy.h',
         'shell/renderer/test_runner/web_content_settings.cc',
         'shell/renderer/test_runner/web_content_settings.h',
         'shell/renderer/test_runner/web_frame_test_proxy.h',
         'shell/renderer/test_runner/web_task.cc',
@@ skipping 887 matching lines @@
                 '--input_symbol', '<(PRODUCT_DIR)/content_shell.exe.pdb',
                 '--destination_dir', '<(dest_dir)',
               ],
             },
           ],
         },
       ],
     }],  # OS=="win" and fastbuild==0 and target_arch=="ia32"
   ]
 }