Optimize build dependency for chrome/renderer and chrome/child

v8_context_snapshot is not necessary when compiling.
This allows to compile chrome/renderer and chrome/child before snapshot is made.

Change-Id: I41fee7c51982dcb34bc7b66d31e6d701d6a24aeb
Reviewed-on: https://chromium-review.googlesource.com/1013886Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551670}

chrome/child/BUILD.gn

@@ -17,10 +17,13 @@ static_library("child") {
     "//chrome/common:buildflags",
     "//content/public/child",
     "//gin",
-    "//tools/v8_context_snapshot",
     "//v8",
   ]
 
+  data_deps = [
+    "//tools/v8_context_snapshot",
+  ]
+
   if (is_win) {
     deps += [ "//components/crash/content/app:crash_export_thunk_include" ]
   }

chrome/renderer/BUILD.gn

@@ -164,11 +164,14 @@ static_library("renderer") {
     "//third_party/icu",
     "//third_party/re2",
     "//third_party/widevine/cdm:headers",
-    "//tools/v8_context_snapshot",
     "//ui/surface",
     "//v8:v8",
   ]
 
+  data_deps = [
+    "//tools/v8_context_snapshot",
+  ]
+
   configs += [ "//build/config/compiler:wexit_time_destructors" ]
 
   if (enable_nacl) {