Pull in ICU 4.2.1 with the fix for a memory leak in i18n/timezone.cpp

BUG=8198
TEST=net-purify test passes on Windows
TBR=erikkay
Review URL: http://codereview.chromium.org/196061

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@25713 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -25,7 +25,7 @@ deps = {
     "/trunk/deps/third_party/WebKit@20601",
 
   "src/third_party/icu":
-    "/trunk/deps/third_party/icu42@25651",
+    "/trunk/deps/third_party/icu42@25712",
 
   "src/third_party/hunspell":
    "/trunk/deps/third_party/hunspell128@25668",