mojo/public: Include gtest.h as "gtest/gtest.h", instead of via "absolute" path.

mojo/public/c/tests/compile/compile_unittest.cc

 // Copyright 2013 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.
 
 // This file just "forwards" to "pure" tests -- those that are written using
 // only headers from mojo/public/c/include/mojo,
 // mojo/public/c/include/mojo/environment, mojo/public/c/include/mojo/system
 // (and the C standard library), and not using gtest.
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "gtest/gtest.h"
 
 // Defined in compile_unittest_pure_c.c.
 extern "C" const char* MinimalCTest(void);
 
 // Defined in compile_unittest_pure_cpp.cc.
 const char* MinimalCppTest();
 
 namespace {
 
 // This checks that things actually work in C (not C++).
 TEST(CompileTest, MinimalCTest) {
   const char* failure = MinimalCTest();
   EXPECT_FALSE(failure) << failure;
 }
 
 // This checks that things compile in C++ as well, without gtest.
 TEST(CompileTest, MinimalCppTest) {
   const char* failure = MinimalCppTest();
   EXPECT_FALSE(failure) << failure;
 }
 
 }  // namespace