Add support for reading .gypi files.

tools/gn/functions.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/functions.h"
 
 #include <iostream>
 
 #include "base/environment.h"
 #include "base/strings/string_util.h"
@@ skipping 336 matching lines @@
     // Passed an identifier "defined(foo)".
     if (scope->GetValue(identifier->value().value()))
       return Value(function, true);
     return Value(function, false);
   }
 
   const AccessorNode* accessor = args_vector[0]->AsAccessor();
   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);
     }
   }
 
   // Argument is invalid.
   *err = Err(function, "Bad thing passed to defined().",
       "It should be of the form defined(foo) or defined(foo.bar).");
   return Value();
 }
 
@@ skipping 340 matching lines @@
     return found_function->second.executed_block_runner(
         function, args.list_value(), &block_scope, err);
   }
 
   // Otherwise it's a no-block function.
   return found_function->second.no_block_runner(scope, function,
                                                 args.list_value(), err);
 }
 
 }  // namespace functions