Use different icons for the overlay and non-overlay cast buttons

We want the overlay cast icon to be visible on all backgrounds, so its
background has to be at least semi-opaque. The non-overlay cast icon,
however, should have the same background as the media controls, which
is easiest to achive by making its background transparent. As such we
need different icons for the two cases.

This CL simply provides the new icons. The corresponding Blink CL, which
uses them, is https://codereview.chromium.org/716613002.

BUG=426373

Review URL: https://codereview.chromium.org/711083002

Cr-Commit-Position: refs/heads/master@{#303620}

content/app/resources/content_resources.grd

@@ -47,6 +47,7 @@
       <structure type="chrome_scaled_image" name="IDR_MEDIAPLAYER_FULLSCREEN_BUTTON_DISABLED" file="mediaplayer_fullscreen_disabled.png" />
       <structure type="chrome_scaled_image" name="IDR_MEDIAPLAYER_CAST_BUTTON_OFF" file="mediaplayer_cast_off.png" />
       <structure type="chrome_scaled_image" name="IDR_MEDIAPLAYER_CAST_BUTTON_ON" file="mediaplayer_cast_on.png" />
+      <structure type="chrome_scaled_image" name="IDR_MEDIAPLAYER_OVERLAY_CAST_BUTTON_OFF" file="mediaplayer_overlay_cast_off.png" />
       <structure type="chrome_scaled_image" name="IDR_MEDIAPLAYER_OVERLAY_PLAY_BUTTON" file="mediaplayer_overlay_play.png" />
       <if expr="is_macosx">
         <structure type="chrome_scaled_image" name="IDR_OVERHANG_PATTERN" file="overhang_pattern.png" />

content/child/blink_platform_impl.cc

@@ -812,6 +812,8 @@ const DataResource kDataResources[] = {
     IDR_MEDIAPLAYER_CAST_BUTTON_ON, ui::SCALE_FACTOR_100P },
   { "mediaplayerFullscreenDisabled",
     IDR_MEDIAPLAYER_FULLSCREEN_BUTTON_DISABLED, ui::SCALE_FACTOR_100P },
+  { "mediaplayerOverlayCastOff",
+    IDR_MEDIAPLAYER_OVERLAY_CAST_BUTTON_OFF, ui::SCALE_FACTOR_100P },
   { "mediaplayerOverlayPlay",
     IDR_MEDIAPLAYER_OVERLAY_PLAY_BUTTON, ui::SCALE_FACTOR_100P },
 #if defined(OS_MACOSX)