predictors: db tool workaround to solve sqlite3 compatibility problem.

Current version of python sqilte3 library hasn't support of views. But new
sqlite3 binary used in chrome implicitly creates MmapStatus view everytime that
causes incompatibility problem. This workaround creates a temporary copy of
given database and deletes the view through sqlite3 command line tool that has
support of views.

BUG=631966

Review-Url: https://codereview.chromium.org/2620053002
Cr-Commit-Position: refs/heads/master@{#442945}

tools/resource_prefetch_predictor/prefetch_predictor_tool.py

@@ -13,6 +13,7 @@ adb pull \
 
 import argparse
 import sqlite3
+import os
 
 from resource_prefetch_predictor_pb2 import (PrefetchData, ResourceData)
 
@@ -77,6 +78,15 @@ class Entry(object):
         continue
       self._PrettyPrintResource(resource)
 
+# The version of python sqlite3 library we have in Ubuntu 14.04 LTS doesn't
+# support views but command line util does.
+# TODO(alexilin): get rid of this when python sqlite3 adds view support.
+def CreateCompatibleDatabaseCopy(filename):
+  import tempfile, shutil, subprocess
+  _, tmpfile = tempfile.mkstemp()
+  shutil.copy2(filename, tmpfile)
+  subprocess.call(['sqlite3', tmpfile, 'DROP VIEW MmapStatus'])
+  return tmpfile
 
 def DatabaseStats(filename, domain):
   connection = sqlite3.connect(filename)
@@ -94,7 +104,12 @@ def main():
                       help='Path to the database')
   parser.add_argument('-d', dest='domain', default=None, help='Domain')
   args = parser.parse_args()
-  DatabaseStats(args.database_filename, args.domain)
+  try:
+    database_copy = CreateCompatibleDatabaseCopy(args.database_filename)
+    DatabaseStats(database_copy, args.domain)
+  finally:
+    if os.path.exists(database_copy):
+      os.remove(database_copy)
 
 
 if __name__ == '__main__':