Roll chromium_revision 255773:260462

This disables GN use for the moment (Chromium
has disabled it for now but plan to pick up the
work at a later stage). I'm leaving the rest of
the GN stuff in our DEPS since that's how
the Chromium DEPS currently looks like.

Overview of changes in Chrome DEPS:
$ svn diff http://src.chromium.org/chrome/trunk/src/DEPS -r 255773:260462

which can be compared with the output of:
$ svn cat http://webrtc.googlecode.com/svn/trunk/DEPS | grep chromium_deps | sed 's/^ *//' | sort | uniq

in a WebRTC checkout, gives the following relevant changes:
* third_party/android_tools 0582bd:ca3567
* third_party/icu 249466:259309
* third_party/libjpeg_turbo 251747:259851
* third_party/libyuv 979:986
* third_party/nss 254867:259440
* tools/gyp 1860:1880

The following also shows that Clang is upgraded from r198389 to r202554:
$ svn diff http://src.chromium.org/chrome/trunk/src/tools/clang/scripts/update.sh -r 255773:260462

TEST=trybots
BUG=None
R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/10679004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5822 4adac7df-926f-26a2-2b94-8c16560cd09d

DEPS

@@ -11,7 +11,7 @@ vars = {
   "googlecode_url": "http://%s.googlecode.com/svn",
   "sourceforge_url": "http://svn.code.sf.net/p/%(repo)s/code",
   "chromium_trunk" : "http://src.chromium.org/svn/trunk",
-  "chromium_revision": "255773",
+  "chromium_revision": "260462",
 
   # A small subset of WebKit is needed for the Android Python test framework.
   "webkit_trunk": "http://src.chromium.org/blink/trunk",
@@ -291,11 +291,10 @@ hooks = [
     ],
   },
   {
-    # Pull clang on mac. If nothing changed, or on non-mac platforms, this takes
-    # zero seconds to run. If something changed, it downloads a prebuilt clang.
+    # Pull clang if on Mac or clang is requested via GYP_DEFINES.
     "pattern": ".",
     "action": ["python", Var("root_dir") + "/tools/clang/scripts/update.py",
-               "--mac-only"],
+               "--if-needed"],
   },
   {
     # Download test resources, i.e. video and audio files from Google Storage.