Ready to enable MSan build for PDFium

Add all the necessary files used for MSan build and run.

BUG=pdfium:1

Review-Url: https://codereview.chromium.org/2384353002
diff --git a/.gitignore b/.gitignore
index 154b6f2..c7facb8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@
 /third_party/android_ndk
 /third_party/catapult
 /third_party/icu
+/third_party/instrumented_libraries
 /third_party/llvm
 /third_party/llvm-build
 /third_party/skia