Add Jinja2 macro for adding trailing strings.

third_party/WebKit/Source/build/scripts/templates/macros.tmpl

Index: third_party/WebKit/Source/build/scripts/templates/macros.tmpl
diff --git a/third_party/WebKit/Source/build/scripts/templates/macros.tmpl b/third_party/WebKit/Source/build/scripts/templates/macros.tmpl
index 17a9f4952f510ce1664c028439103e7c6cf4fc56..2357d8fd09085f94cc241f01987d97535367f31e 100644
--- a/third_party/WebKit/Source/build/scripts/templates/macros.tmpl
+++ b/third_party/WebKit/Source/build/scripts/templates/macros.tmpl
@@ -55,3 +55,8 @@ case {{ length }}:
 {% endfor %}
 }
 {% endmacro %}
+
+
+{% macro trailing(loop, str) -%}

[meade_UTC10, 2017/02/13 06:19:58]

Would it make sense to pass in loop.last here instead of passing in loop? It
made me double take a little on why loop is being passed into trailing()
above...

[shend, 2017/02/13 06:40:37]

Hmm, my intention for this macro is to print a string based on the current loop
state. If I make it take in loop.last (i.e. a bool), then the macro kinda
becomes print_if_true(bool, str). It's also less typing for the caller :P. Would
it help if I added an explanatory comment here?

[meade_UTC10, 2017/02/13 06:51:15]

Hmm, it's really print_if_false right? I think it's actually clearer to name it
what it does - which is clearer about what's happening?


{% for field in fields %}
  {{field.name}}({{default_value(field)}}){{trailing(loop, ',')}}
{% endfor %}



{% for field in fields %}
  {{field.name}}({{default_value(field)}}){{print_if_false(loop.last, ',')}}
{% endfor %}

+{% if not loop.last %}{{str}}{% endif %}
+{%- endmacro %}