Roll trace-viewer dep to r251.

DEPS

 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 
 vars = {
   # Use this googlecode_url variable only if there is an internal mirror for it.
   # If you do not know, use the full path while defining your new deps entry.
   "googlecode_url": "http://%s.googlecode.com/svn",
   "sourceforge_url": "http://%(repo)s.svn.sourceforge.net/svnroot/%(repo)s",
   "webkit_trunk": "http://src.chromium.org/blink/trunk",
   "nacl_trunk": "http://src.chromium.org/native_client/trunk",
@@ skipping 61 matching lines @@
   "src/testing/gtest":
     (Var("googlecode_url") % "googletest") + "/trunk@629",
 
   "src/testing/gmock":
     (Var("googlecode_url") % "googlemock") + "/trunk@410",
 
   "src/third_party/angle":
     (Var("googlecode_url") % "angleproject") + "/trunk@2040",
 
   "src/third_party/trace-viewer":
-    (Var("googlecode_url") % "trace-viewer") + "/trunk@245",
+    (Var("googlecode_url") % "trace-viewer") + "/trunk@251",
 
   # Note that this is *not* where we check out WebKit -- this just
   # puts some extra files into place for the real WebKit checkout to
   # happen.  See lines mentioning "webkit_revision" for the real
   # WebKit checkout.
   "src/third_party/WebKit":
     "/trunk/deps/third_party/WebKit@76115",
 
   "src/third_party/icu":
     "/trunk/deps/third_party/icu46@182486",
@@ skipping 612 matching lines @@
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
   {
     # Check for landmines (reasons to clobber the build).
     "pattern": ".",
     "action": ["python", "src/build/landmines.py"],
   },
 ]