Adding presubmit check for WeakPtrFactory in the code

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 8ec7f5323e1e58ee875963b91ec25c82353f54c5..b3b2606c28788857f555f113cf0c725f341cd55d 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -1282,6 +1282,55 @@ def _CheckNoDeprecatedJS(input_api, output_api):
   return results
 
 
+def _CheckForWeakPtrOrder(input_api, output_api):
+  """Check for weakptrfactory order in .h files using ChangedContents."""
+  problems = []
+  warnings = []
+  for f in input_api.AffectedFiles():
+    if not f.LocalPath().endswith(('.cc', '.cpp', '.h', '.mm')):
+      continue
+    contents = f.NewContents()
+    weak_ptr_flag = False
+    change_line_num = 0
+    for line_num, line in f.ChangedContents():
+      change_line_num = line_num
+      break
+    curr_line = 0
+    change_flag = False
+    for line in contents:
+      curr_line += 1
+      if (curr_line != change_line_num) and (change_flag != True):
+        continue
+      else:
+        change_flag = True
+      if 'base::WeakPtrFactory' in line:
+        weak_ptr_flag = True
+        continue
+      if weak_ptr_flag == True:
+        #Checking for commented line
+        strip_line = line.strip()
+        if strip_line.startswith('//'):
+          continue
+        #Check for emptyline for skipping
+        if (len(line.strip()) == 0):
+          continue
+        #Check for valid attributes after the WeakPtrFactory pointer
+        if input_api.re.search(r'(};|\bDISALLOW_COPY_AND_ASSIGN\b)', line):
+          break
+        else:
+          weak_ptr_flag = False
+          problems.append('    %s:%d' % (f.LocalPath(), line_num))
+          break
+
+  if not problems:
+    return []
+  return [output_api.PresubmitError(
+    'Member variables should appear before the WeakPtrFactory, to ensure '
+    'that any WeakPtrs to Controller are \ninvalidated before its members '
+    'variable\'s destructors are executed, rendering them invalid.',
+    problems)]
+
+
 def _CommonChecks(input_api, output_api):
   """Checks common to both upload and commit."""
   results = []
@@ -1325,6 +1374,7 @@ def _CommonChecks(input_api, output_api):
   results.extend(_CheckParseErrors(input_api, output_api))
   results.extend(_CheckForIPCRules(input_api, output_api))
 
+  results.extend(_CheckForWeakPtrOrder(input_api, output_api))
   if any('PRESUBMIT.py' == f.LocalPath() for f in input_api.AffectedFiles()):
     results.extend(input_api.canned_checks.RunUnitTestsInDirectory(
         input_api, output_api,