tools/gn: rename char_offset to column_number

tools/gn/parse_tree_unittest.cc

Index: tools/gn/parse_tree_unittest.cc
diff --git a/tools/gn/parse_tree_unittest.cc b/tools/gn/parse_tree_unittest.cc
index 29a0faf36f951890f5475f1416908c3d3e5deceb..cf8d8e9a5fabc2c924e6ff28ec09c8baffd54128 100644
--- a/tools/gn/parse_tree_unittest.cc
+++ b/tools/gn/parse_tree_unittest.cc
@@ -90,7 +90,7 @@ TEST(ParseTree, BlockUnusedVars) {
   // origin will point to the value assigned to the variable (in this case, the
   // "13" assigned to "b".
   EXPECT_EQ(3, err.location().line_number());
-  EXPECT_EQ(7, err.location().char_offset());
+  EXPECT_EQ(7, err.location().column_number());
 }
 
 TEST(ParseTree, OriginForDereference) {
@@ -107,7 +107,7 @@ TEST(ParseTree, OriginForDereference) {
   // The origin for the "not a string" error message should be where the value
   // was dereferenced (the "a" on the second line).
   EXPECT_EQ(2, err.location().line_number());
-  EXPECT_EQ(20, err.location().char_offset());
+  EXPECT_EQ(20, err.location().column_number());
 }
 
 TEST(ParseTree, SortRangeExtraction) {