Switch iOS to pulling Blink headers instead of WebKit headers

iOS should pull the new Blink headers used by all the other platforms
now that the mirror repo exists.

The old WebKit header pull will be removed once nothing references
headers in those locations any more.

BUG=242829
R=blundell@chromium.org

Review URL: https://codereview.chromium.org/15931004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202905 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -410,6 +410,9 @@ deps_os = {
     "src/third_party/WebKit/Source/Platform/chromium/public":
       Var("ios_webkit_trunk") + "/Source/Platform/chromium/public@" +
       Var("ios_webkit_revision"),
+    # Pull only the headers from Blink.
+    "src/third_party/WebKit/public":
+      Var("webkit_trunk") + "/public@" + Var("webkit_revision"),
 
     # Code that's not needed due to not building everything (especially WebKit).
     "src/build/util/support": None,