Reland Auto-generate v8 version based on tags.

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 67886bcee89a766f00061790b8287193d0eb730a..7bf4794a7cdc35d704b0a1845e828c0dbaf71366 100644
--- a/DEPS
+++ b/DEPS
@@ -88,6 +88,13 @@ hooks = [
     'action': ['python', 'v8/tools/clang/scripts/update.py', '--if-needed'],
   },
   {
+    # Generate v8 version based on the last git tag.
+    "pattern": ".",
+    "action": ["python",
+               "v8/tools/push-to-trunk/generate_version.py",
+               "--hook"],
+  },
+  {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "v8/build/gyp_v8"],