Update gtest and gmock to 1.8.x.

This applies parts of https://crrev.com/469551 and
https://crrev.com/471303 to PDFium.

Change-Id: Ifbb8e4c300bd276fe3c6fe60d19ebb1618be8936
Reviewed-on: https://pdfium-review.googlesource.com/28791
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
diff --git a/.gitignore b/.gitignore
index 830cb6e..a1b0405 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,13 +3,12 @@
 /buildtools
 /out
 /testing/corpus
-/testing/gmock
-/testing/gtest
 /third_party/android_ndk
 /third_party/binutils
 /third_party/catapult
 /third_party/depot_tools
 /third_party/freetype/src
+/third_party/googletest/src
 /third_party/icu
 /third_party/instrumented_libraries
 /third_party/jinja2