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

snapshot_toolchain.gni

Index: snapshot_toolchain.gni
diff --git a/WATCHLISTS b/snapshot_toolchain.gni
similarity index 66%
copy from WATCHLISTS
copy to snapshot_toolchain.gni
index f57dfa140258f3ab10bf3ccd37bdb48c5d151e87..c419c3ff06c5abdf729d2a5d971addbe769f9b74 100644
--- a/WATCHLISTS
+++ b/snapshot_toolchain.gni
@@ -1,4 +1,4 @@
-# Copyright 2013 the V8 project authors. All rights reserved.
+# 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:
@@ -25,34 +25,22 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-# Watchlist Rules
-# Refer: http://dev.chromium.org/developers/contributing-code/watchlists
+# The snapshot needs to be compiled for the host, but compiled with
+# a toolchain that matches the bit-width of the target.
 
-# IMPORTANT: The regular expression filepath is tested against each path using
-# re.search, so it is not usually necessary to add .*.
+# 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
+}
 
-{
-  'WATCHLIST_DEFINITIONS': {
-    'public_api': {
-      'filepath': 'include/',
-    },
-    'snapshot': {
-      'filepath': 'src/snapshot/',
-    },
-    'debugger': {
-      'filepath': 'src/debug/',
-    },
-  },
 
-  'WATCHLISTS': {
-    'public_api': [
-      'phajdan.jr@chromium.org',
-    ],
-    'snapshot': [
-      'yangguo@chromium.org',
-    ],
-    'debugger': [
-      'yangguo@chromium.org',
-    ],
-  },
-}