Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/277effe..d9a25a7

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

Change-Id: I34d9dab2d4ae63e589b7a4af78438fce4d8e71f3
Reviewed-on: https://chromium-review.googlesource.com/581890Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46825}

DEPS

@@ -8,7 +8,7 @@ vars = {
 
 deps = {
   "v8/build":
-    Var("chromium_url") + "/chromium/src/build.git" + "@" + "277effef1fee496ae92426e3b0f59eaa645bfe81",
+    Var("chromium_url") + "/chromium/src/build.git" + "@" + "d9a25a7a65b3c71330e2aa2cdbb2ebd7d44357f5",
   "v8/tools/gyp":
     Var("chromium_url") + "/external/gyp.git" + "@" + "d61a9397e668fa9843c4aa7da9e79460fe590bfb",
   "v8/third_party/icu":