Fix WebGLDebugShaders::getTranslatedShaderSource returning null

Source/core/html/canvas/WebGLDebugShaders.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 40 matching lines @@
 {
     return adoptRef(new WebGLDebugShaders(context));
 }
 
 String WebGLDebugShaders::getTranslatedShaderSource(WebGLShader* shader)
 {
     if (isLost())
         return String();
     if (!m_context->validateWebGLObject("getTranslatedShaderSource", shader))
         return "";
-    return m_context->webGraphicsContext3D()->getTranslatedShaderSourceANGLE(shader->object());
+    return m_context->ensureNotNull(m_context->webGraphicsContext3D()->getTranslatedShaderSourceANGLE(shader->object()));
 }
 
 bool WebGLDebugShaders::supported(WebGLRenderingContextBase* context)
 {
     return context->extensionsUtil()->supportsExtension("GL_ANGLE_translated_shader_source");
 }
 
 const char* WebGLDebugShaders::extensionName()
 {
     return "WEBGL_debug_shaders";
 }
 
 } // namespace WebCore