Make ActionMailer frozen string literal friendly.

actionmailer/test/base_test.rb

@@ -120,7 +120,7 @@ class BaseTest < ActiveSupport::TestCase
     email = BaseMailer.attachment_with_hash
     assert_equal(1, email.attachments.length)
     assert_equal("invoice.jpg", email.attachments[0].filename)
-    expected = "\312\213\254\232)b"
+    expected = "\312\213\254\232)b".dup
     expected.force_encoding(Encoding::BINARY)
     assert_equal expected, email.attachments["invoice.jpg"].decoded
   end
@@ -129,7 +129,7 @@ class BaseTest < ActiveSupport::TestCase
     email = BaseMailer.attachment_with_hash_default_encoding
     assert_equal(1, email.attachments.length)
     assert_equal("invoice.jpg", email.attachments[0].filename)
-    expected = "\312\213\254\232)b"
+    expected = "\312\213\254\232)b".dup
     expected.force_encoding(Encoding::BINARY)
     assert_equal expected, email.attachments["invoice.jpg"].decoded
   end

actionpack/lib/action_dispatch/http/response.rb

@@ -103,7 +103,7 @@ module ActionDispatch # :nodoc:
 
       def body
         @str_body ||= begin
-          buf = ""
+          buf = "".dup
           each { |chunk| buf << chunk }
           buf
         end

actionpack/lib/action_dispatch/journey/router/utils.rb

@@ -14,7 +14,7 @@ module ActionDispatch
         #   normalize_path("/%ab")  # => "/%AB"
         def self.normalize_path(path)
           encoding = path.encoding
-          path = "/#{path}"
+          path = "/#{path}".dup
           path.squeeze!("/".freeze)
           path.sub!(%r{/+\Z}, "".freeze)
           path.gsub!(/(%[a-f0-9]{2})/) { $1.upcase }

actionview/lib/action_view/template.rb

@@ -282,7 +282,7 @@ module ActionView
 
         # Make sure that the resulting String to be eval'd is in the
         # encoding of the code
-        source = <<-end_src
+        source = <<-end_src.dup
           def #{method_name}(local_assigns, output_buffer)
             _old_virtual_path, @virtual_path = @virtual_path, #{@virtual_path.inspect};_old_output_buffer = @output_buffer;#{locals_code};#{code}
           ensure
@@ -334,7 +334,7 @@ module ActionView
 
       def method_name
         @method_name ||= begin
-          m = "_#{identifier_method_name}__#{@identifier.hash}_#{__id__}"
+          m = "_#{identifier_method_name}__#{@identifier.hash}_#{__id__}".dup
           m.tr!("-".freeze, "_".freeze)
           m
         end

actionview/lib/action_view/template/resolver.rb

@@ -14,7 +14,7 @@ module ActionView
       alias_method :partial?, :partial
 
       def self.build(name, prefix, partial)
-        virtual = ""
+        virtual = "".dup
         virtual << "#{prefix}/" unless prefix.empty?
         virtual << (partial ? "_#{name}" : name)
         new name, prefix, partial, virtual