IDL: Make caching lex table robust

Source/bindings/scripts/blink_idl_parser.py

Index: Source/bindings/scripts/blink_idl_parser.py
diff --git a/Source/bindings/scripts/blink_idl_parser.py b/Source/bindings/scripts/blink_idl_parser.py
index 0120654a5f44083573025fb02f43aaec2876e8aa..37c62c5669b952fb11c730fee264a5f8cefc4418 100644
--- a/Source/bindings/scripts/blink_idl_parser.py
+++ b/Source/bindings/scripts/blink_idl_parser.py
@@ -95,6 +95,19 @@ for rule in REMOVED_RULES:
     production_name = 'p_' + rule
     delattr(IDLParser, production_name)
 
+# The base name of cached lexer table generated by BlinkIDLLexer
+LEX_TABLE_BASENAME = 'lextab'
+
+
+def remove_cached_lex_table(outputdir):
+    table_files = [
+        os.path.join(outputdir, '%s.py' % LEX_TABLE_BASENAME),
+        os.path.join(outputdir, '%s.pyc' % LEX_TABLE_BASENAME),
+    ]
+    for table_file in table_files:
+        if os.path.exists(table_file):
+            os.unlink(table_file)
+
 
 class BlinkIDLParser(IDLParser):
     # [1]
@@ -440,12 +453,16 @@ class BlinkIDLParser(IDLParser):
 ################################################################################
 
 def main(argv):
-    # If file itself executed, cache parse table
+    # If file itself executed, cache parse table. Caching the parse table
+    # also caches lex table. Before caching these tables, we remove the
+    # previous cached lex table if exists so that the build system can keep
+    # track of dependencies. See http://crbug.com/397909
     try:
         outputdir = argv[1]
     except IndexError as err:
         print 'Usage: %s OUTPUT_DIR' % argv[0]
         return 1
+    remove_cached_lex_table(outputdir)
     # Important: rewrite_tables=True causes the cache file to be deleted if it
     # exists, thus making sure that PLY doesn't load it instead of regenerating
     # the parse table.