fix build break (missing file in IAccessible2Proxy)

I removed the _p.c files from the associated iaccessible2 previously to fix windows incremental link, but didn't add the required _p.c one to the proxy dll.

BUG=Red tree
TEST=IAccessible2Proxy links

Review URL: http://codereview.chromium.org/7649003
Patch from scottmg@chromium.org <scottmg@chromium.org>.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@96675 0039d316-1c4b-4281-b951-d872f2087c98

third_party/iaccessible2/iaccessible2.gyp

@@ -38,6 +38,7 @@
       'sources': [
         'IAccessible2Proxy.def',
         '<(INTERMEDIATE_DIR)/../iaccessible2/dlldata.c',
+        '<(INTERMEDIATE_DIR)/../iaccessible2/ia2_api_all_p.c',
       ],
       'link_settings': {
         'libraries': [