Revert of Explicit control in tools of ANGLE frontend and backend

tools/flags/SkCommonFlagsConfig.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SK_COMMON_FLAGS_CONFIG_H
 #define SK_COMMON_FLAGS_CONFIG_H
 
 #include "SkCommandLineFlags.h"
 
 #if SK_SUPPORT_GPU
 #include "GrContextFactory.h"
 #endif
 
 DECLARE_string(config);
 
 #if SK_SUPPORT_GPU
 class SkCommandLineConfigGpu;
 #endif
 
 // SkCommandLineConfig represents a Skia rendering configuration string.
 // The string has following form:
 // tag:
 //   [via-]*backend
-// where 'backend' consists of chars excluding hyphen
+// where 'backend' consists of chars excluding hyphen or "angle-gl"
 // and each 'via' consists of chars excluding hyphen.
 class SkCommandLineConfig {
   public:
     SkCommandLineConfig(const SkString& tag, const SkString& backend,
                         const SkTArray<SkString>& viaParts);
     virtual ~SkCommandLineConfig();
 #if SK_SUPPORT_GPU
     virtual const SkCommandLineConfigGpu* asConfigGpu() const { return nullptr; }
 #endif
     const SkString& getTag() const { return fTag; }
@@ skipping 35 matching lines @@
     SkColorType fColorType;
     sk_sp<SkColorSpace> fColorSpace;
 };
 #endif
 
 typedef SkTArray<SkAutoTDelete<SkCommandLineConfig>, true> SkCommandLineConfigArray;
 void ParseConfigs(const SkCommandLineFlags::StringArray& configList,
                   SkCommandLineConfigArray* outResult);
 
 #endif