cc: Only register live tiles with the TileManager

cc: Only register live tiles with the TileManager

Instead of registering a tile with the TileManager when it is
created, only do so when the tile has a non-zero chance of
being rasterized.

Use a self-owned scoped_refptr to specify that a ManagedTilesState
may not be freed (e.g, because it is being painted) instead of a
bool because the ManagedTileState may now be unregistered at any
point (even during painting).

BUG=165852

[ccameron, 2013-02-16 14:47:52]

This is patch 2 of 3 patches which make the TileManager only be aware of the
alive tiles. This is the change that actually has the effect on the tile count.

The 3rd patch removes the all_tiles_/live_or_allocated_tiles_ distinction and
uses a list directly for insertion/removal/sorting. I haven't been able to
definitively prove that that strictly improves performance. I'll put that one
up later.

Also of note is that this uses scoped_refptr<> a lot. It looks like that
structure
is thread-safe, so I'd like some reassurance that it isn't death for performance
(and if it is, a suggested alternative that doesn't give any thread safety 
guarantees).

[reveman, 2013-02-19 01:43:51]

On 2013/02/16 14:47:52, ccameron1 wrote:
> Also of note is that this uses scoped_refptr<> a lot. It looks like that
> structure
> is thread-safe, so I'd like some reassurance that it isn't death for
performance
> (and if it is, a suggested alternative that doesn't give any thread safety 
> guarantees).

I'd assume scoped_refptr<> is only affected by thread-safe related code when
used with RefCountedThreadSafe objects.