Create PaintChunk and begin writing code to build paint chunks.

BUG=537409

Review URL: https://codereview.chromium.org/1379883003

Cr-Commit-Position: refs/heads/master@{#352369}
void DisplayItemList::invalidateUntracked(DisplayItemClient client)
{
    ASSERT(m_newDisplayItems.isEmpty());
    updateValidlyCachedClientsIfNeeded();
    m_validlyCachedClients.remove(client);
}

void DisplayItemList::invalidateUntracked(DisplayItemClient client)
{
    ASSERT(m_newDisplayItems.isEmpty());
    updateValidlyCachedClientsIfNeeded();
    m_validlyCachedClients.remove(client);
}
