Reland Auto-generate v8 version based on tags.

DEPS

 # Note: The buildbots evaluate this file with CWD set to the parent
 # directory and assume that the root of the checkout is in ./v8/, so
 # all paths in here must match this assumption.
 
 vars = {
   "git_url": "https://chromium.googlesource.com",
 }
 
 deps = {
   "v8/build/gyp":
@@ skipping 70 matching lines @@
     ],
   },
   {
     # Pull clang if needed or requested via GYP_DEFINES.
     # Note: On Win, this should run after win_toolchain, as it may use it.
     'name': 'clang',
     'pattern': '.',
     '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"],
   },
 ]