Mac: Don't crash in -[AcceleratedPluginView drawView] when the RWHVMac went away.

chrome/browser/renderer_host/render_widget_host_view_mac.mm

Index: chrome/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/chrome/browser/renderer_host/render_widget_host_view_mac.mm b/chrome/browser/renderer_host/render_widget_host_view_mac.mm
index 9e5c6e7db94b3f17d470b068a0677dbb0ab5241c..68435a2bdc8d7b9ace56ccc99dec77d0a8568770 100644
--- a/chrome/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/chrome/browser/renderer_host/render_widget_host_view_mac.mm
@@ -283,9 +283,11 @@ static CVReturn DrawOneAcceleratedPluginCallback(
   // Called on a background thread. Synchronized via the CGL context lock.
   CGLLockContext(cglContext_);
 
-  // TODO(thakis): Pixel or view coordinates for size?
-  renderWidgetHostView_->DrawAcceleratedSurfaceInstance(
-      cglContext_, pluginHandle_, [self cachedSize]);
+  if (renderWidgetHostView_) {
+    // TODO(thakis): Pixel or view coordinates for size?
+    renderWidgetHostView_->DrawAcceleratedSurfaceInstance(
+        cglContext_, pluginHandle_, [self cachedSize]);
+  }
 
   CGLFlushDrawable(cglContext_);
   CGLUnlockContext(cglContext_);