Roll DEPS for build, buildtools, and instrumented_lib.

To update to recent revisions, this CL also does the following to DEPS:
- Pulls in depot_tools to third_party/.
- Update hooks for instrumented_libraries to download by default.
- Add checkout_configuration variables so one can skip the download.

The instrumented libraries are large downloads. https://crrev.com/507438
contains notes on how to avoid them.

TBR=dpranke@chromium.org

Change-Id: Ice0f9fcff0d2c8fba5fd3e1ef3e04e94b6bda710
Reviewed-on: https://pdfium-review.googlesource.com/21390
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/.gitignore b/.gitignore
index beeb3cd..830cb6e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@
 /third_party/android_ndk
 /third_party/binutils
 /third_party/catapult
+/third_party/depot_tools
 /third_party/freetype/src
 /third_party/icu
 /third_party/instrumented_libraries