Move find_depot_tools.py to build/

tools/safely-roll-deps.py

Index: tools/safely-roll-deps.py
diff --git a/tools/safely-roll-deps.py b/tools/safely-roll-deps.py
index 7c64aaee6cb0882212370c84c5fcdfd4a2ce89e3..739412387963acf50d84c38c236b7dca402c8993 100755
--- a/tools/safely-roll-deps.py
+++ b/tools/safely-roll-deps.py
@@ -14,6 +14,9 @@ import os
 import re
 import sys
 
+SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
+SRC_DIR = os.path.abspath(os.path.join(SCRIPT_DIR, os.pardir))
+sys.path.insert(0, os.path.join(SRC_DIR, 'build'))
 import find_depot_tools
 import scm
 import subprocess2