<webview>: Fix missing transparency in captureVisibleRegion().

extensions/browser/api/guest_view/web_view/web_view_internal_api.cc

Index: extensions/browser/api/guest_view/web_view/web_view_internal_api.cc
diff --git a/extensions/browser/api/guest_view/web_view/web_view_internal_api.cc b/extensions/browser/api/guest_view/web_view/web_view_internal_api.cc
index 0b8d4afe4189b786f959568c532e1069c369ebe4..0514fa2865ea2919c9f22e3bd9c0884fff78af51 100644
--- a/extensions/browser/api/guest_view/web_view/web_view_internal_api.cc
+++ b/extensions/browser/api/guest_view/web_view/web_view_internal_api.cc
@@ -273,6 +273,7 @@ bool WebViewInternalCaptureVisibleRegionFunction::RunAsyncSafe(
     image_details = ImageDetails::FromValue(*spec);
   }
 
+  is_guest_transparent_ = guest->allow_transparency();
   return CaptureAsync(guest->web_contents(), image_details.get(),
                       base::Bind(&WebViewInternalCaptureVisibleRegionFunction::
                                      CopyFromBackingStoreComplete,
@@ -283,6 +284,10 @@ bool WebViewInternalCaptureVisibleRegionFunction::IsScreenshotEnabled() {
   return true;
 }
 
+bool WebViewInternalCaptureVisibleRegionFunction::ClientAllowsTransparency() {
+  return is_guest_transparent_;
+}
+
 void WebViewInternalCaptureVisibleRegionFunction::OnCaptureSuccess(
     const SkBitmap& bitmap) {
   std::string base64_result;