Update Google Test to v1.10.0 (#840)

This commit updates the version of Google Test from 1.8 to 1.10.

test/gtest-1.10.0/googletest/docs/samples.md

@@ -0,0 +1,22 @@
+# Googletest Samples {#samples}
+
+If you're like us, you'd like to look at
+[googletest samples.](https://github.com/google/googletest/tree/master/googletest/samples)
+The sample directory has a number of well-commented samples showing how to use a
+variety of googletest features.
+
+*   Sample #1 shows the basic steps of using googletest to test C++ functions.
+*   Sample #2 shows a more complex unit test for a class with multiple member
+    functions.
+*   Sample #3 uses a test fixture.
+*   Sample #4 teaches you how to use googletest and `googletest.h` together to
+    get the best of both libraries.
+*   Sample #5 puts shared testing logic in a base test fixture, and reuses it in
+    derived fixtures.
+*   Sample #6 demonstrates type-parameterized tests.
+*   Sample #7 teaches the basics of value-parameterized tests.
+*   Sample #8 shows using `Combine()` in value-parameterized tests.
+*   Sample #9 shows use of the listener API to modify Google Test's console
+    output and the use of its reflection API to inspect test results.
+*   Sample #10 shows use of the listener API to implement a primitive memory
+    leak checker.