Add option cc_wrapper to GN

build/toolchain/cc_wrapper.gni

Index: build/toolchain/cc_wrapper.gni
diff --git a/build/toolchain/ccache.gni b/build/toolchain/cc_wrapper.gni
similarity index 53%
rename from build/toolchain/ccache.gni
rename to build/toolchain/cc_wrapper.gni
index 806e079a4cbca9a5b62a6454570a7f7fd093fb6c..1fa185019ca0d44c71334d7528916719df2c38df 100644
--- a/build/toolchain/ccache.gni
+++ b/build/toolchain/cc_wrapper.gni
@@ -2,11 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# Defines the configuration of ccache - a c/c++ compiler cache which can
-# greatly reduce recompilation times.
+# Defines the configuration of cc wrapper
+# ccache: a c/c++ compiler cache which can greatly reduce recompilation times.
+# icecc, distcc: it takes compile jobs from a build and distributes them among
+#                remote machines allowing a parallel build.
 #
-# TIPS:
+# TIPS
 #
+# 1) ccache
 # Set clang_use_chrome_plugins=false if using ccache 3.1.9 or earlier, since
 # these versions don't support -Xclang.  (3.1.10 and later will silently
 # ignore -Xclang, so it doesn't matter if you disable clang_use_chrome_plugins
@@ -18,8 +21,15 @@
 # To avoid -Wparentheses-equality clang warnings, at some cost in terms of
 # speed, you can do:
 # export CCACHE_CPP2=yes
+#
+# 2) icecc
+# Set clang_use_chrome_plugins=false because icecc cannot distribute custom
+# clang libraries.
+#
+# To use icecc and ccache together, set cc_wrapper = "ccache" with
+# export CCACHE_PREFIX=icecc
 
 declare_args() {
-  # Set to true to enable ccache.  Probably doesn't work on windows.
-  use_ccache = false
+  # Set to "ccache", "icecc" or "distcc".  Probably doesn't work on windows.
+  cc_wrapper = ""
 }