Roll buildtools a9e946f166..e0b3d0a721

  In order to roll GN 0fbf0789..ccbeab67 (r555198:r558753) and pick up
  the following changes:

  443b70db Fix GN doc formatting.
  e8a3ce91 GN: do not make indirect dependency to direct dependency
  ea15ea06 Fully move PathService into the base namespace.
  ae62ba99 GN: Make the linker output file depend on the inputs.
  629ba73c [MessageLoop] Fix message_loop.h includes

TBR=brettw@chromium.org

Change-Id: I982bbe01bad86a66e7aed379ee1155bdfaa76ff8
Reviewed-on: https://chromium-review.googlesource.com/1060095
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558795}

DEPS

@@ -112,7 +112,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
   # and whatever else without interference from each other.
-  'buildtools_revision': 'a9e946f166b73f9dc170129f6586a1e68efb0ab3',
+  'buildtools_revision': 'e0b3d0a721330fd4831b109cd432fa1c5cb3d16f',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.