Use default_args for configuring V8.

Removes the values in build_overrides/v8.gni and uses the new default_args in
the "//.gn" file to set these arguments.

Once all places are updated, we can remove build_overrides/v8.gni.

BUG=684096

Review-Url: https://codereview.chromium.org/2648233006
Cr-Commit-Position: refs/heads/master@{#446124}

.gn

@@ -12,6 +12,32 @@ buildconfig = "//build/config/BUILDCONFIG.gn"
 # in the source tree, e.g. for third party source trees.
 secondary_source = "//build/secondary/"
 
+# These arguments override the default values for items in a declare_args
+# block. "gn args" in turn can override these.
+#
+# In general the value for a build arg in the declare_args block should be the
+# default. In some cases, a DEPS-ed in project will want different defaults for
+# being built as part of Chrome vs. being built standalone. In this case, the
+# Chrome defaults should go here. There should be no overrides here for
+# values declared in the main Chrome repository.
+default_args = {
+  v8_extra_library_files = [
+    # Dependencies used by the extra libraries. Putting them here causes them
+    # to be executed first during snapshot creation.
+    "//third_party/WebKit/Source/core/streams/CommonStrings.js",
+
+    # Extra libraries.
+    "//third_party/WebKit/Source/core/streams/ByteLengthQueuingStrategy.js",
+    "//third_party/WebKit/Source/core/streams/CountQueuingStrategy.js",
+    "//third_party/WebKit/Source/core/streams/ReadableStream.js",
+  ]
+  v8_experimental_extra_library_files =
+      [ "//third_party/WebKit/Source/core/streams/WritableStream.js" ]
+  v8_enable_inspector = true
+  v8_enable_gdbjit = false
+  v8_imminent_deprecation_warnings = false
+}
+
 # These are the targets to check headers for by default. The files in targets
 # matching these patterns (see "gn help label_pattern" for format) will have
 # their includes checked for proper dependencies when you run either

build_overrides/v8.gni

@@ -2,26 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# V8 extras
-# Adding V8 extras files requires API owners review
+# This file should be empty.
 
-# This list is for files that export symbols that are used in other extras
-# files. Putting them here causes them to be executed first during snapshot
-# creation.
-_v8_extras_dependencies =
-    [ "//third_party/WebKit/Source/core/streams/CommonStrings.js" ]
-
-_v8_extras = [
-  "//third_party/WebKit/Source/core/streams/ByteLengthQueuingStrategy.js",
-  "//third_party/WebKit/Source/core/streams/CountQueuingStrategy.js",
-  "//third_party/WebKit/Source/core/streams/ReadableStream.js",
-]
-
-v8_extra_library_files = _v8_extras_dependencies + _v8_extras
-
-v8_experimental_extra_library_files =
-    [ "//third_party/WebKit/Source/core/streams/WritableStream.js" ]
-
-v8_enable_inspector_override = true
-v8_enable_gdbjit_default = false
-v8_imminent_deprecation_warnings_default = false
+# TODO(brettw) http://crbug.com/684096 Remove this when all callers are updated
+# to use the new build overrides system.