Add simplejson 2.1.0 and use it when it's not already installed.

third_party/simplejson/LICENSE.txt

Index: third_party/simplejson/LICENSE.txt
diff --git a/third_party/simplejson/LICENSE.txt b/third_party/simplejson/LICENSE.txt
new file mode 100644
index 0000000000000000000000000000000000000000..ad95f29c172aaf259fc3adb087b2d3dd021f10ad
--- /dev/null
+++ b/third_party/simplejson/LICENSE.txt
@@ -0,0 +1,19 @@
+Copyright (c) 2006 Bob Ippolito
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.