Split the GN 'snapshot_toolchain' logic out into an include file.

We need to build parts of v8 with a toolchain that might be different
from both the default (target) toolchain and the regular host toolchain,
because we need the snapshot to have the same bit-width as the target.
V8's build defines a 'snapshot_toolchain' setting for this.

It turns out that we need the value of this toolchain to be exposed
to the Chromium build because some of the test targets (in browser_tests)
depend on d8 and need to be able to built using the same toolchain.

R=brett@chromium.org, jochen@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1350223004

Cr-Commit-Position: refs/heads/master@{#30854}

BUILD.gn

@@ -11,6 +11,8 @@ import("//build/config/sanitizers/sanitizers.gni")
 # Chromium build.
 import("//build/module_args/v8.gni")
 
+import("snapshot_toolchain.gni")
+
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_deprecation_warnings = false
@@ -35,24 +37,6 @@ if (is_msan) {
   v8_target_arch = target_cpu
 }
 
-# The snapshot needs to be compiled for the host, but compiled with
-# a toolchain that matches the bit-width of the target.
-#
-# TODO(GYP): For now we only support 32-bit little-endian target builds from an
-# x64 Linux host. Eventually we need to support all of the host/target
-# configurations v8 runs on.
-if (host_cpu == "x64" && host_os == "linux") {
-  if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
-    snapshot_toolchain = "//build/toolchain/linux:clang_x86"
-  } else if (target_cpu == "x64") {
-    snapshot_toolchain = "//build/toolchain/linux:clang_x64"
-  } else {
-    assert(false, "Need environment for this arch")
-  }
-} else {
-  snapshot_toolchain = default_toolchain
-}
-
 ###############################################################################
 # Configurations
 #
@@ -1792,6 +1776,7 @@ if (is_component_build) {
 }
 
 if ((current_toolchain == host_toolchain && v8_toolset_for_d8 == "host") ||
+    (current_toolchain == snapshot_toolchain && v8_toolset_for_d8 == "host") ||
     (current_toolchain != host_toolchain && v8_toolset_for_d8 == "target")) {
   executable("d8") {
     sources = [

snapshot_toolchain.gni

+# Copyright 2015 the V8 project authors. All rights reserved.
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+#       notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+#       copyright notice, this list of conditions and the following
+#       disclaimer in the documentation and/or other materials provided
+#       with the distribution.
+#     * Neither the name of Google Inc. nor the names of its
+#       contributors may be used to endorse or promote products derived
+#       from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# The snapshot needs to be compiled for the host, but compiled with
+# a toolchain that matches the bit-width of the target.
+
+# TODO(GYP): For now we only support 32-bit little-endian target builds from an
+# x64 Linux host. Eventually we need to support all of the host/target
+# configurations v8 runs on.
+if (host_cpu == "x64" && host_os == "linux") {
+  if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
+    snapshot_toolchain = "//build/toolchain/linux:clang_x86"
+  } else if (target_cpu == "x64") {
+    snapshot_toolchain = "//build/toolchain/linux:clang_x64"
+  } else {
+    assert(false, "Need environment for this arch")
+  }
+} else {
+  snapshot_toolchain = default_toolchain
+}
+
+