Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/fb6dc3a..725734c

TBR=machenbach@chromium.org,hablich@chromium.org,sergiyb@chromium.org

Change-Id: I1f42691e880f0c9e038fb66ca7d2aa07a7cd6514
Reviewed-on: https://chromium-review.googlesource.com/1034217
Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52873}

DEPS

@@ -12,7 +12,7 @@ vars = {
 
 deps = {
   'v8/build':
-    Var('chromium_url') + '/chromium/src/build.git' + '@' + 'fb6dc3aba5f080908acb63b6dcd544c25051d793',
+    Var('chromium_url') + '/chromium/src/build.git' + '@' + '725734cd9c9fef3258b1ce28552c3ab144c093eb',
   'v8/tools/gyp':
     Var('chromium_url') + '/external/gyp.git' + '@' + 'd61a9397e668fa9843c4aa7da9e79460fe590bfb',
   'v8/third_party/icu':