[swarming] Add luci-go's isolate tool, downloaded via runhooks.

Port https://codereview.chromium.org/1154633003/

BUG=chromium:535160
LOG=n

Review URL: https://codereview.chromium.org/1380983002

Cr-Commit-Position: refs/heads/master@{#31045}

.gitignore

@@ -78,6 +78,9 @@ shell_g
 /tools/clang
 /tools/jsfunfuzz
 /tools/jsfunfuzz.zip
+/tools/luci-go/linux64/isolate
+/tools/luci-go/mac64/isolate
+/tools/luci-go/win64/isolate.exe
 /tools/oom_dump/oom_dump
 /tools/oom_dump/oom_dump.o
 /tools/swarming_client

DEPS

@@ -93,6 +93,40 @@ hooks = [
                 "-s", "v8/buildtools/linux64/clang-format.sha1",
     ],
   },
+  # Pull luci-go binaries (isolate, swarming) using checked-in hashes.
+  {
+    'name': 'luci-go_win',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=win32',
+                '--no_auth',
+                '--bucket', 'chromium-luci',
+                '-d', 'v8/tools/luci-go/win64',
+    ],
+  },
+  {
+    'name': 'luci-go_mac',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=darwin',
+                '--no_auth',
+                '--bucket', 'chromium-luci',
+                '-d', 'v8/tools/luci-go/mac64',
+    ],
+  },
+  {
+    'name': 'luci-go_linux',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=linux*',
+                '--no_auth',
+                '--bucket', 'chromium-luci',
+                '-d', 'v8/tools/luci-go/linux64',
+    ],
+  },
   # Pull binutils for linux, enabled debug fission for faster linking /
   # debugging when used with clang on Ubuntu Precise.
   # https://code.google.com/p/chromium/issues/detail?id=352046

tools/luci-go/linux64/isolate.sha1

+32a3d49a4f7279ad022f346f7d960b2d58e2a0fe
\ No newline at end of file

tools/luci-go/mac64/isolate.sha1

+83306c575904ec92c1af9ccc67240d26069df337
\ No newline at end of file

tools/luci-go/win64/isolate.exe.sha1

+da358c2666ef9b89022e0eadf363cc6e123384e2
\ No newline at end of file