fix third_party_headers to work properly on Windows w/ ninja.

webkit/support/setup_third_party.gyp

 # 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': {
     'setup_third_party_cmd': ['python', 'setup_third_party.py'],
     'webkit_client_api_dest': '<(SHARED_INTERMEDIATE_DIR)/webkit/third_party/WebKit/Source/WebKit/chromium/public',
     'platform_api_dest': '<(SHARED_INTERMEDIATE_DIR)/webkit/third_party/WebKit/Source/Platform/chromium/public',
     'mac_webcoresupport_dest': '<(SHARED_INTERMEDIATE_DIR)/webkit/third_party/WebKit/Source/WebKit/mac/WebCoreSupport',
   },
   'targets': [
     {
+      # This target is only invoked when we are building chromium inside
+      # of a WebKit checkout. In this case, we will have chromium files
+      # that include WebKit headers via third_party/WebKit/Source/... ;
+      # that directory doesn't exist in a chromium-inside-webkit
+      # checkout, and so we need to create sets of forwarding headers.
+      #
+      # In addition, we can hit limits on the include paths on windows
+      # with a regular forwarding header due to the deep directory
+      # hierarchies, and so rather than using #includes that are relative
+      # to the directory containing the generated header, the generated files
+      # use #includes that are relative to <(DEPTH).
       'target_name': 'third_party_headers',
       'type': 'none',
       'direct_dependent_settings': {
         'include_dirs': [
           '<(SHARED_INTERMEDIATE_DIR)/webkit',
+          '<(DEPTH)',
         ],
       },
       'actions': [
         {
           'action_name': 'third_party_webkit_client_api_forwarding_headers',
           'inputs': [
             '<!@(<(setup_third_party_cmd) inputs <(DEPTH)/public)',
             'setup_third_party.py',
           ],
           'outputs': [
             "<!@(<(setup_third_party_cmd) outputs <(DEPTH)/public '<(webkit_client_api_dest)')",
           ],
           'action': [
             '<@(setup_third_party_cmd)',
             'setup_headers',
             '<(DEPTH)/public',
             '<(webkit_client_api_dest)',
+            '<(DEPTH)',
           ],
           'message': 'Generating forwarding headers for third_party/WebKit/Source/WebKit/chromium/public',
         },
         {
         'action_name': 'third_party_platform_api_forwarding_headers',
           'inputs': [
             '<!@(<(setup_third_party_cmd) inputs <(DEPTH)/../../Platform/chromium/public)',
             'setup_third_party.py',
           ],
           'outputs': [
@@ skipping 19 matching lines @@
                 'setup_third_party.py',
               ],
               'outputs': [
                 "<!@(<(setup_third_party_cmd) outputs <(DEPTH)/../mac/WebCoreSupport '<(mac_webcoresupport_dest)')",
               ],
               'action': [
                 '<@(setup_third_party_cmd)',
                 'setup_headers',
                 '<(DEPTH)/../mac/WebCoreSupport',
                 '<(mac_webcoresupport_dest)',
+                '<(DEPTH)',
               ],
               'message': 'Generating forwarding headers for third_party/WebKit/Source/WebKit/mac/WebCoreSupport',
             },
           ],
         }],
       ],
     },
   ],
 }