[Bindings] Create and use V8 context snapshots

content/public/app/mojo/content_renderer_manifest.json

 {
   "name": "content_renderer",
   "display_name": "Content (renderer process)",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "browser": [
           "content::mojom::Child",
           "content::mojom::EmbeddedWorkerInstanceClient",
           "content::mojom::EmbeddedWorkerSetup",
@@ skipping 57 matching lines @@
       "path": "snapshot_blob.bin",
       "platform": "linux"
     }],
     "v8_snapshot_32_data" : [{
       "path": "assets/snapshot_blob_32.bin",
       "platform": "android"
     }],
     "v8_snapshot_64_data" : [{
       "path": "assets/snapshot_blob_64.bin",
       "platform": "android"
-    }]
+    }],
+    "v8_context_snapshot_data" : [
+      {
+        "path": "v8_context_snapshot.bin",

[dcheng, 2017/07/12 09:55:09]

Nit: please use spaces

[peria, 2017/07/12 10:30:37]

Done.

+        "platform": "linux"
+      },
+      {
+        "path": "assets/v8_context_snapshot.bin",

[dcheng, 2017/07/12 09:55:09]

Just to confirm: these assets are read-only? It's not possible for a rogue
renderer to modify the snapshot?

(Sorry if this is a silly question, this is the first time I've seen changes
like this: based on the fact that this is already used by other things, I assume
that this must be true. It's just not very obvious to me why it's true)

[peria, 2017/07/12 10:30:37]

Yes, they are read-only.

+        "platform": "android"
+      }
+    ]
   }
 }