Make build incremental

runtime/tools/create_snapshot_bin.py

Index: runtime/tools/create_snapshot_bin.py
diff --git a/runtime/tools/create_snapshot_bin.py b/runtime/tools/create_snapshot_bin.py
index 19c29434b77199e17e958bc3ae8b1263f6984d84..b91de38e86353a40e7e1ed131e3840161aeda87b 100755
--- a/runtime/tools/create_snapshot_bin.py
+++ b/runtime/tools/create_snapshot_bin.py
@@ -52,6 +52,10 @@ def BuildOptions():
   result.add_option("--abi",
       action="store", type="string",
       help="Desired ABI for android target OS. armeabi-v7a or x86")
+  result.add_option("--timestamp_file",
+      action="store", type="string",
+      help="Path to timestamp file that will be written",
+      default="")
   return result
 
 
@@ -71,6 +75,14 @@ def ProcessOptions(options):
   return True
 
 
+def CreateTimestampFile(options):
+  if options.timestamp_file != '':
+    dir_name = os.path.dirname(options.timestamp_file)
+    if not os.path.exists(dir_name):
+      os.mkdir(dir_name)
+    open(options.timestamp_file, 'w').close()
+
+
 def Main():
   # Parse options.
   parser = BuildOptions()
@@ -113,6 +125,9 @@ def Main():
   except Exception as e:
     return -1
 
+  # Success, update timestamp file.
+  CreateTimestampFile(options)
+
   return 0