Frame focus via Capybara::Element

Fixes #465.

lib/capybara/webkit/browser.rb

@@ -70,11 +70,13 @@ module Capybara::Webkit
       command("CurrentUrl")
     end
 
-    def frame_focus(frame_id_or_index=nil)
-      if frame_id_or_index.is_a? Fixnum
-        command("FrameFocus", "", frame_id_or_index.to_s)
-      elsif frame_id_or_index
-        command("FrameFocus", frame_id_or_index)
+    def frame_focus(selector=nil)
+      if selector.respond_to?(:base)
+        selector.base.invoke('focus')
+      elsif selector.is_a? Fixnum
+        command("FrameFocus", "", selector.to_s)
+      elsif selector
+        command("FrameFocus", selector)
       else
         command("FrameFocus")
       end

lib/capybara/webkit/driver.rb

@@ -82,8 +82,8 @@ module Capybara::Webkit
       browser.resize_window(width, height)
     end
 
-    def within_frame(frame_id_or_index)
-      browser.frame_focus(frame_id_or_index)
+    def within_frame(selector)
+      browser.frame_focus(selector)
       begin
         yield
       ensure

spec/driver_spec.rb

@@ -72,6 +72,14 @@ describe Capybara::Webkit::Driver do
       end
     end
 
+    it "finds frames by element" do
+      frame = driver.find('//iframe').first
+      element = double(Capybara::Node::Base, base: frame)
+      driver.within_frame(element) do
+        driver.find("//*[contains(., 'goodbye')]").should_not be_empty
+      end
+    end
+
     it "raises error for missing frame by index" do
       expect { driver.within_frame(1) { } }.
         to raise_error(Capybara::Webkit::InvalidResponseError)