Allow to have a transparent UA dependent background.

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index 6b7de27e113664c4cc383bfcdd08755dfbfea254..818cb446eb204b85643a423af239fe51bf7bfebf 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -1382,6 +1382,7 @@ bool RenderViewImpl::OnMessageReceived(const IPC::Message& message) {
     IPC_MESSAGE_HANDLER(ViewMsg_MoveOrResizeStarted, OnMoveOrResizeStarted)
     IPC_MESSAGE_HANDLER(ViewMsg_ClearFocusedElement, OnClearFocusedElement)
     IPC_MESSAGE_HANDLER(ViewMsg_SetBackgroundOpaque, OnSetBackgroundOpaque)
+    IPC_MESSAGE_HANDLER(ViewMsg_SetBackgroundColor, OnSetBackgroundColor)
     IPC_MESSAGE_HANDLER(ViewMsg_EnablePreferredSizeChangedMode,
                         OnEnablePreferredSizeChangedMode)
     IPC_MESSAGE_HANDLER(ViewMsg_EnableAutoResize, OnEnableAutoResize)
@@ -2787,6 +2788,11 @@ void RenderViewImpl::OnSetBackgroundOpaque(bool opaque) {
     compositor_->setHasTransparentBackground(!opaque);
 }
 
+void RenderViewImpl::OnSetBackgroundColor(SkColor color) {
+  webview()->setBaseBackgroundColor(color);
+  compositor_->setBackgroundColor(color);
+}
+
 void RenderViewImpl::OnSetActive(bool active) {
   if (webview())
     webview()->setIsActive(active);