Add Window#fullscreen and support in Selenium driver

lib/capybara/driver/base.rb

@@ -90,7 +90,11 @@ class Capybara::Driver::Base
   end
 
   def maximize_window(handle)
-    raise Capybara::NotSupportedByDriverError, 'Capybara::Driver::Base#maximize_current_window'
+    raise Capybara::NotSupportedByDriverError, 'Capybara::Driver::Base#maximize_window'
+  end
+
+  def fullscreen_window(handle)
+    raise Capybara::NotSupportedByDriverError, 'Capybara::Driver::Base#fullscreen_window'
   end
 
   def close_window(handle)

lib/capybara/selenium/driver.rb

@@ -217,7 +217,18 @@ class Capybara::Selenium::Driver < Capybara::Driver::Base
       if marionette? && (window_size(handle) == [width, height])
         {}
       else
-        browser.manage.window.resize_to(width, height)
+        begin
+          browser.manage.window.resize_to(width, height)
+        rescue Selenium::WebDriver::Error::UnknownError => e
+          if chrome? && e.message =~ /failed to change window state/
+            # Chromedriver doesn't wait long enough for state to change when coming out of fullscreen
+            # and raises unnecessary error. Wait a bit and try again.
+            sleep 0.5
+            browser.manage.window.resize_to(width, height)
+          else
+            raise
+          end
+        end
       end
     end
   end
@@ -229,6 +240,22 @@ class Capybara::Selenium::Driver < Capybara::Driver::Base
     sleep 0.1 # work around for https://code.google.com/p/selenium/issues/detail?id=7405
   end
 
+  def fullscreen_window(handle)
+    within_given_window(handle) do
+      window = browser.manage.window
+      bridge = browser.send(:bridge)
+
+      if bridge.respond_to?(:full_screen_window)
+        window.full_screen
+      elsif chrome?
+        result = bridge.http.call(:post, "session/#{bridge.session_id}/window/fullscreen", {})
+        result['value']
+      else
+        raise Capybara::NotSupportedByDriverError, "Fullscreen is not supported by Capybara::Selenium::Driver for #{browser_name}"
+      end
+    end
+  end
+
   def close_window(handle)
     raise ArgumentError, "Not allowed to close the primary window" if handle == window_handles.first
     within_given_window(handle) do

lib/capybara/spec/session/window/window_spec.rb

@@ -184,4 +184,21 @@ Capybara::SpecHelper.spec Capybara::Window, requires: [:windows] do
       expect(ow_height).to be > 300
     end
   end
+
+  describe '#fullscreen' do
+    before do
+      @initial_size = @session.current_window.size
+    end
+
+    after do
+      @session.current_window.resize_to(*@initial_size)
+      sleep 0.5
+    end
+
+    it "should be able to fullscreen the window" do
+      expect do
+        @session.current_window.fullscreen
+      end.not_to raise_error
+    end
+  end
 end

lib/capybara/window.rb

@@ -101,6 +101,17 @@ module Capybara
       wait_for_stable_size { @driver.maximize_window(handle) }
     end
 
+    ##
+    # Fullscreen window.
+    #
+    # If a particular driver doesn't have concept of fullscreen it may not support this method.
+    #
+    # @macro about_current
+    #
+    def fullscreen
+      @driver.fullscreen_window(handle)
+    end
+
     def eql?(other)
       other.is_a?(self.class) && @session == other.session && @handle == other.handle
     end