depot_tools: Use git-checkout instead of git-rebase.

Changes like crrev.com/c/1752507, where a file that was previously in
.gitignore becomes part of the repo, makes update_depot_tools fail
to rebase.

Use git checkout origin/master instead.

Bug: 996359
Change-Id: Ib1a43b8842cebce96ab1fabaedc8e5653b9a708e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1764708
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>

update_depot_tools

@@ -101,12 +101,11 @@ function update_git_repo {
 
   git fetch -q origin &> /dev/null
   local REBASE_TXT STATUS
-  REBASE_TXT=$(git rebase -q origin/master 2>&1)
+  CHECKOUT_TXT=$(git checkout origin/master 2>&1)
   STATUS=$?
   if [[ $STATUS -ne 0 ]]; then
     echo "depot_tools update failed. Conflict in $base_dir" >&2
-    echo "$REBASE_TXT" >&2
-    git rebase --abort 2> /dev/null
+    echo "$CHECKOUT_TXT" >&2
   fi
   return $STATUS
 }

update_depot_tools.bat

@@ -51,7 +51,7 @@ for /F %%x in ('git config --get remote.origin.url') DO (
   )
 )
 call git fetch -q origin > NUL
-call git rebase -q origin/master > NUL
+call git checkout origin/master > NUL
 if errorlevel 1 (
   echo Failed to update depot_tools.
   goto :EOF