[build] Add fuchsia sdk download to DEPS

TBR=sergiyb@chromium.org

Bug: chromium:772816
Change-Id: I40014d381637394057b0646740a2487fef5fe8a6
Reviewed-on: https://chromium-review.googlesource.com/711841Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48443}

DEPS

@@ -283,6 +283,16 @@ hooks = [
     'pattern': '.',
     'action': ['python', 'v8/tools/clang/scripts/update.py'],
   },
+  {
+    'name': 'fuchsia_sdk',
+    'pattern': '.',
+    'condition': 'checkout_fuchsia',
+    'action': [
+      'python',
+      'v8/build/fuchsia/update_sdk.py',
+      '226f6dd0cad1d6be63a353ce2649423470729ae9',
+    ],
+  },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     'pattern': '.',