Added null check for shader source when compiling, and fixed re-caching behavior to spec

gpu/command_buffer/service/program_manager.cc

 // Copyright (c) 2012 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 "gpu/command_buffer/service/program_manager.h"
 
 #include <algorithm>
 #include <set>
 #include <utility>
 #include <vector>
@@ skipping 364 matching lines @@
     const std::string* mapped_name = GetAttribMappedName(it->first);
     if (mapped_name && *mapped_name != it->first)
       glBindAttribLocation(service_id_, it->second, mapped_name->c_str());
   }
 }
 
 void ProgramManager::DoCompileShader(ShaderManager::ShaderInfo* info,
                                      ShaderTranslator* translator,
                                      FeatureInfo* feature_info) {
   if (program_cache_ &&
-      program_cache_->GetShaderCompilationStatus(*info->source()) ==
+      program_cache_->GetShaderCompilationStatus(info->source() ?
+                                                 *info->source() : "") ==
           ProgramCache::COMPILATION_SUCCEEDED) {
     info->SetStatus(true, "", translator);
     info->FlagSourceAsCompiled(false);
     return;
   }
   ForceCompileShader(info->source(), info, translator, feature_info);
 }
 
 void ProgramManager::ForceCompileShader(const std::string* source,
                                         ShaderManager::ShaderInfo* info,
@@ skipping 717 matching lines @@
     info->ClearUniforms(&zero_);
   }
 }
 
 int32 ProgramManager::MakeFakeLocation(int32 index, int32 element) {
   return index + element * 0x10000;
 }
 
 }  // namespace gles2
 }  // namespace gpu