REGRESSION(r175642) Caused webkit unit tests failures

Chromium revision r175642 broke the webkit unit tests at webkit.org
http://wkb.ug/106631 because GetWebKitRootDir() returns a file path
that contains a relative "../.." component on some webkit bots.

Make webkit_support::GetWebKitRootDir() return an absolute path.

TEST=webkit unit tests pass
BUG=http://wkb.ug/106631

Review URL: https://chromiumcodereview.appspot.com/12038003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@177931 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/webkit/support/webkit_support.cc b/webkit/support/webkit_support.cc
index 6e85925..2dd97e4 100644
--- a/webkit/support/webkit_support.cc
+++ b/webkit/support/webkit_support.cc
@@ -468,6 +468,7 @@
 
 WebKit::WebString GetWebKitRootDir() {
   FilePath path = GetWebKitRootDirFilePath();
+  CHECK(file_util::AbsolutePath(&path));
   std::string path_ascii = path.MaybeAsASCII();
   CHECK(!path_ascii.empty());
   return WebKit::WebString::fromUTF8(path_ascii.c_str());