Implement window management devtools commands for headless.

headless/public/headless_browser.h

Index: headless/public/headless_browser.h
diff --git a/headless/public/headless_browser.h b/headless/public/headless_browser.h
index 92b2610abd15be9500f13331b24a691e168aba85..c1834c4e16af7327392f54851acc98e7c2987016 100644
--- a/headless/public/headless_browser.h
+++ b/headless/public/headless_browser.h
@@ -164,10 +164,14 @@ struct HEADLESS_EXPORT HeadlessBrowser::Options {
   // chrome::switches::kHostRules for a description for the format.
   std::string host_resolver_rules;
 
-  // Default window size. This is also used to create the window tree host and
-  // as initial screen size. Defaults to 800x600.
+  // Default window size. This is also used to create the window tree host.
+  // Defaults to 800x600.
   gfx::Size window_size;
 
+  // Screen size. This is used to initialize screen size for web_contents and
+  // support window management devtools commands. Defaults to 1,920x1,080.

[Sami, 2017/05/22 16:30:57]

This isn't reflected to JavaScript (i.e., screen.width/height) as far as I can
tell. Maybe add a TODO for that?

+  gfx::Size screen_size;
+
   // Path to user data directory, where browser will look for its state.
   // If empty, default directory (where the binary is located) will be used.
   base::FilePath user_data_dir;