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

chrome/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <QuartzCore/QuartzCore.h>
 
 #include "chrome/browser/renderer_host/render_widget_host_view_mac.h"
 
 #include "app/app_switches.h"
 #include "app/surface/io_surface_support_mac.h"
@@ skipping 265 matching lines @@
   if (renderWidgetHostView_)
     renderWidgetHostView_->DeallocFakePluginWindowHandle(pluginHandle_);
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   [super dealloc];
 }
 
 - (void)drawView {
   // 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_);
 }
 
 - (void)onRenderWidgetHostViewGone {
   CGLLockContext(cglContext_);
   // Deallocate the plugin handle while we still can.
   renderWidgetHostView_->DeallocFakePluginWindowHandle(pluginHandle_);
   renderWidgetHostView_ = NULL;
@@ skipping 2212 matching lines @@
   if (!string) return NO;
 
   // If the user is currently using an IME, confirm the IME input,
   // and then insert the text from the service, the same as TextEdit and Safari.
   [self confirmComposition];
   [self insertText:string];
   return YES;
 }
 
 @end