Add support for reading .gypi files.

tools/gn/functions.cc

Index: tools/gn/functions.cc
diff --git a/tools/gn/functions.cc b/tools/gn/functions.cc
index ac1c29492d15be5817f560f9ba02066c1dc99f0e..c8ae4690c2043f6332985503e996297c4b145611 100644
--- a/tools/gn/functions.cc
+++ b/tools/gn/functions.cc
@@ -354,16 +354,26 @@ Value RunDefined(Scope* scope,
   if (accessor) {
     // Passed an accessor "defined(foo.bar)".
     if (accessor->member()) {
-      // The base of the accessor must be a scope if it's defined.
+      // The base of the accessor must be a scope/dict if it's defined.
       const Value* base = scope->GetValue(accessor->base().value());
       if (!base)
         return Value(function, false);
-      if (!base->VerifyTypeIs(Value::SCOPE, err))
+      if (base->type() == Value::SCOPE) {
+        // Check the member inside the scope to see if its defined.
+        if (base->scope_value()->GetValue(accessor->member()->value().value()))
+          return Value(function, true);
+      } else if (base->type() == Value::DICT) {
+        // Check the dictionary to see if the member is present.
+        if (base->dict_value().find(
+                accessor->member()->value().value().as_string()) !=
+            base->dict_value().end())
+          return Value(function, true);
+      } else {
+        *err = Err(function,
+            std::string("Type \"") + Value::DescribeType(base->type()) +
+            "\" is not usable with the '.' operator.");
         return Value();
-
-      // Check the member inside the scope to see if its defined.
-      if (base->scope_value()->GetValue(accessor->member()->value().value()))
-        return Value(function, true);
+      }
       return Value(function, false);
     }
   }