Added viewport meta tag to about:flags

http://crbug.com/232102 added --enable-viewport-meta to allow desktop
browsers to experimentally honor the viewport <meta> tag. This CL adds
the flag to the about:flags page so it can easily be turned on.

BUG=329996

Review URL: https://codereview.chromium.org/123303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243301 0039d316-1c4b-4281-b951-d872f2087c98

chrome/app/generated_resources.grd

@@ -6385,6 +6385,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_CONTACTS_DESCRIPTION" desc="Description of the 'Enable contacts' lab.">
         Enables downloading Google contacts and displaying them in the App List.
       </message>
+      <message name="IDS_FLAGS_ENABLE_VIEWPORT_META_NAME" desc="Name of the flag to turn on viewport meta tag support.">
+        Enable viewport meta tag.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_VIEWPORT_META_DESCRIPTION" desc="Description of the flag to turn on viewport meta tag support.">
+        Enables handling of the viewport meta tag to allow pages to set the layout width and user zoom properties.
+      </message>
 
       <if expr="pp_ifdef('chromeos')">
         <message name="IDS_FLAGS_ALLOW_TOUCHPAD_THREE_FINGER_CLICK_NAME" desc="Name for the flag to enable touchpad three finger click as middle button.">

chrome/browser/about_flags.cc

@@ -1115,6 +1115,13 @@ const Experiment kExperiments[] = {
     SINGLE_VALUE_TYPE(cc::switches::kEnablePinchVirtualViewport),
   },
 #endif  // defined(USE_ASH)
+  {
+    "enable-viewport-meta",
+    IDS_FLAGS_ENABLE_VIEWPORT_META_NAME,
+    IDS_FLAGS_ENABLE_VIEWPORT_META_DESCRIPTION,
+    kOsLinux | kOsWin | kOsCrOS | kOsMac,
+    SINGLE_VALUE_TYPE(switches::kEnableViewportMeta),
+  },
 #if defined(OS_CHROMEOS)
   {
     "disable-boot-animation",