Utilize Python context managers for opening/closing files

In some of these cases, files were not being closed

components/script/dom/bindings/codegen/BindingGen.py

@@ -39,9 +39,8 @@ def main():
     webIDLFile = os.path.normpath(args[2])
 
     # Load the parsing results
-    f = open('ParserResults.pkl', 'rb')
-    parserData = cPickle.load(f)
-    f.close()
+    with open('ParserResults.pkl', 'rb') as f:
+        parserData = cPickle.load(f)
 
     # Create the configuration data.
     config = Configuration(configFile, parserData)

components/script/dom/bindings/codegen/CodegenRust.py

@@ -41,18 +41,16 @@ def replaceFileIfChanged(filename, newContents):
 
     # oldFileContents = ""
     # try:
-    #     oldFile = open(filename, 'rb')
-    #     oldFileContents = ''.join(oldFile.readlines())
-    #     oldFile.close()
+    #     with open(filename, 'rb') as oldFile:
+    #         oldFileContents = ''.join(oldFile.readlines())
     # except:
     #     pass
 
     # if newContents == oldFileContents:
     #     return False
 
-    f = open(filename, 'wb')
-    f.write(newContents)
-    f.close()
+    with open(filename, 'wb') as f:
+        f.write(newContents)
 
     return True
 

components/script/dom/bindings/codegen/GenerateCSS2PropertiesWebIDL.py

@@ -18,9 +18,8 @@ for [prop, pref] in propList:
     props += "  [%s] attribute DOMString %s;\n" % (", ".join(extendedAttrs),
                                                    prop)
 
-idlFile = open(sys.argv[1], "r")
-idlTemplate = idlFile.read()
-idlFile.close()
+with open(sys.argv[1], "r") as idlFile:
+    idlTemplate = idlFile.read()
 
 print ("/* THIS IS AN AUTOGENERATED FILE.  DO NOT EDIT */\n\n" +
        string.Template(idlTemplate).substitute({"props": props}))

components/script/dom/bindings/codegen/GlobalGen.py

@@ -47,16 +47,14 @@ def main():
     parser = WebIDL.Parser(options.cachedir)
     for filename in fileList:
         fullPath = os.path.normpath(os.path.join(baseDir, filename))
-        f = open(fullPath, 'rb')
-        lines = f.readlines()
-        f.close()
+        with open(fullPath, 'rb') as f:
+            lines = f.readlines()
         parser.parse(''.join(lines), fullPath)
     parserResults = parser.finish()
 
     # Write the parser results out to a pickle.
-    resultsFile = open('ParserResults.pkl', 'wb')
-    cPickle.dump(parserResults, resultsFile, -1)
-    resultsFile.close()
+    with open('ParserResults.pkl', 'wb') as resultsFile:
+        cPickle.dump(parserResults, resultsFile, -1)
 
     # Load the configuration.
     config = Configuration(configFile, parserResults)