[IndexedDB] Adding transaction and value support to observers

content/browser/indexed_db/indexed_db_connection.h

Index: content/browser/indexed_db/indexed_db_connection.h
diff --git a/content/browser/indexed_db/indexed_db_connection.h b/content/browser/indexed_db/indexed_db_connection.h
index 20acb7b7244c0ed10041c8a59b955c37bf2c2419..3258cf87612221a1f4c6632b57c0e8acc626c76a 100644
--- a/content/browser/indexed_db/indexed_db_connection.h
+++ b/content/browser/indexed_db/indexed_db_connection.h
@@ -77,9 +77,16 @@ class CONTENT_EXPORT IndexedDBConnection {
   // TODO(dmurph): Change that so this doesn't need to ignore unknown ids.
   void RemoveTransaction(int64_t id);
 
+  int64_t NextObserverTransactionId();

[cmumford, 2017/01/09 21:31:25]

Comment for method.

[dmurph, 2017/01/10 00:17:38]

Done.

+
  private:
   const int32_t id_;
 
+  // The renderer-created transactions are in the right 32 bits, and the
+  // browser-created transactions are in the left 32 bits.
+  int64_t next_observer_transaction_id_ = 1ll << 32;

[pwnall, 2017/01/10 01:01:24]

I think it'd be easier to debug if you have the highest bit set on browser
transactions, and unset on renderer transactions.

I think you can have minObserverTransactionId = ~0ll - (~0ll >> 1) and then
start from -1 and decrement on the browser side, and start from 0 (or 1) and
increment on the render side.

Also, IIUC, observer transactions are triggered by renderer transactions
committing. If that's the case, how about having renderer transactions be in 1
... (~0ll >> 1), and having a browser transaction be the negative of the
renderer transaction that triggered it?

[dmurph, 2017/01/10 20:39:59]

That second suggestion wouldn't work as the the same transaction could have
multiple observers requesting transactions on the same connection, so they need
to have multiple unique ids.

I'm mostly working off the pre-existing id constraint here:
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/indexe...,

Where renderer ids are already constrained to the bottom 32 bits. I'd rather
initially keep the ID separation we had previously, and then if necessary do a
follow-up patch to make it nicer.

[pwnall, 2017/01/10 23:21:54]

Thank you for explaining! Sorry, I completely forgot about the multiple
observers case.
I wonder if that comment still relevant. AFAIK, ports were a WebKit thing, and
Chromium's content layer is Blink's only "port".
Works for me. Feel free to file a bug against me instead.

+  static const int64_t kMaxObserverTransactionId = -1ll;

[cmumford, 2017/01/09 21:31:25]

How about moving kMaxObserverTransactionId to the *.cc file to simplify the
interface?

[dmurph, 2017/01/10 00:17:38]

Done.

[pwnall, 2017/01/10 01:01:24]

Hm, I was going to suggest adding a static_assert to make sure that the browser
and the renderer agree on how the transaction ID space is split up.

+
   // The process id of the child process this connection is associated with.
   // Tracked for IndexedDBContextImpl::GetAllOriginsDetails and debugging.
   const int child_process_id_;