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

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

Index: mojo/public/c/tests/compile/compile_unittest.cc
diff --git a/mojo/public/c/tests/compile/compile_unittest.cc b/mojo/public/c/tests/compile/compile_unittest.cc
index 3160edba149ed80f9f3dc45d300284ed6bfc460a..ca1c907bbe95ff822aa27395738b3a5e50898e22 100644
--- a/mojo/public/c/tests/compile/compile_unittest.cc
+++ b/mojo/public/c/tests/compile/compile_unittest.cc
@@ -7,7 +7,7 @@
 // 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);