deps: enable v8 postmortem debugging again

Cherry-pick https://codereview.chromium.org/1033733003 from upstream
and re-enable postmortem debugging.

PR-URL: #1232
Reviewed-By: Fedor Indutny <fedor@indutny.com>

Author: bnoordhuis

common.gypi

@@ -20,17 +20,16 @@
     # Enable disassembler for `--print-code` v8 options
     'v8_enable_disassembler': 1,
 
-    # Disable support for postmortem debugging, continuously broken.
-    'v8_postmortem_support%': 'false',
-
     # Don't bake anything extra into the snapshot.
     'v8_use_external_startup_data%': 0,
 
     'conditions': [
       ['OS == "win"', {
         'os_posix': 0,
+        'v8_postmortem_support%': 'false',
       }, {
         'os_posix': 1,
+        'v8_postmortem_support%': 'true',
       }],
       ['GENERATOR == "ninja" or OS== "mac"', {
         'OBJ_DIR': '<(PRODUCT_DIR)/obj',

deps/v8/tools/gen-postmortem-metadata.py

@@ -91,7 +91,7 @@
     { 'name': 'prop_idx_first',
         'value': 'DescriptorArray::kFirstIndex' },
     { 'name': 'prop_type_field',
-        'value': 'FIELD' },
+        'value': 'DATA' },
     { 'name': 'prop_type_mask',
         'value': 'PropertyDetails::TypeField::kMask' },
     { 'name': 'prop_index_mask',