Add "depot_tools" to DEPS.

Add "depot_tools" to DEPS, and integrate this into "find_depot_tools".
This formally establishes Chromium's dependency on the "depot_tools"
repository and ensures that Chromium's expectations are versioned
alongside "depot_tools"'s revision.

Add a hook to forcefully disable the DEPS'd "depot_tools"'s self-update
mechanism, which is enabled by default for developers, ensuring that it
will remain at the version pinned in DEPS.

Finally, update "find_depot_tools" logic to point to the new DEPS'd
"depot_tools" directly as a priority preference.

Note that other repositories which have their own versions of
"find_depot_tools" will have to have their scripts similarly updated.

BUG=chromium:727917
TEST=local
  - Ran `gclient sync`, syncs and disables.
  - Manually imported "find_depot_tools", successfully finds DEPS'd
    version.
NOTRY=true

Change-Id: I11355ac5c55754b76327a74aa1001bfce4b332ed
Reviewed-on: https://chromium-review.googlesource.com/522802
Commit-Queue: Dirk Pranke <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Reviewed-by: Nodir Turakulov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#477414}
diff --git a/build/find_depot_tools.py b/build/find_depot_tools.py
index 9596d2f..b70ace4 100755
--- a/build/find_depot_tools.py
+++ b/build/find_depot_tools.py
@@ -15,6 +15,10 @@
 import sys
 
 
+# Path to //src
+SRC = os.path.abspath(os.path.join(os.path.dirname(__file__), os.pardir))
+
+
 def IsRealDepotTools(path):
   expanded_path = os.path.expanduser(path)
   return os.path.isfile(os.path.join(expanded_path, 'gclient.py'))
@@ -22,7 +26,13 @@
 
 def add_depot_tools_to_path():
   """Search for depot_tools and add it to sys.path."""
-  # First look if depot_tools is already in PYTHONPATH.
+  # First, check if we have a DEPS'd in "depot_tools".
+  deps_depot_tools = os.path.join(SRC, 'third_party', 'depot_tools')
+  if IsRealDepotTools(deps_depot_tools):
+    sys.path.append(deps_depot_tools)
+    return deps_depot_tools
+
+  # Then look if depot_tools is already in PYTHONPATH.
   for i in sys.path:
     if i.rstrip(os.sep).endswith('depot_tools') and IsRealDepotTools(i):
       return i