headless: Allow both WW,HH and WWxHH forms for specifying window size

As Chrome only supports the former format, change the documentation to
refer to that.

BUG=678539

Review-Url: https://codereview.chromium.org/2622773003
Cr-Commit-Position: refs/heads/master@{#442609}

headless/app/headless_shell.cc

@@ -45,7 +45,7 @@ const char kDefaultScreenshotFileName[] = "screenshot.png";
 
 bool ParseWindowSize(std::string window_size, gfx::Size* parsed_window_size) {
   int width, height = 0;
-  if (sscanf(window_size.c_str(), "%dx%d", &width, &height) >= 2 &&
+  if (sscanf(window_size.c_str(), "%d%*[x,]%d", &width, &height) >= 2 &&
       width >= 0 && height >= 0) {
     parsed_window_size->set_width(width);
     parsed_window_size->set_height(height);

headless/app/headless_shell_switches.cc

@@ -54,7 +54,7 @@ const char kUserDataDir[] = "user-data-dir";
 // specified virtual time budget is exhausted.
 const char kVirtualTimeBudget[] = "virtual-time-budget";
 
-// Sets the initial window size. Provided as string in the format "800x600".
+// Sets the initial window size. Provided as string in the format "800,600".
 const char kWindowSize[] = "window-size";
 
 }  // namespace switches