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::addItemToIndexIfNeeded(const DisplayItem& displayItem, size_t index, DisplayItemIndicesByClientMap& displayItemIndicesByClient)
{
    if (!displayItem.isCacheable())
        return;

    DisplayItemIndicesByClientMap::iterator it = displayItemIndicesByClient.find(displayItem.client());
    Vector<size_t>& indices = it == displayItemIndicesByClient.end() ?
        displayItemIndicesByClient.add(displayItem.client(), Vector<size_t>()).storedValue->value : it->value;
    indices.append(index);
}

void DisplayItemList::addItemToIndexIfNeeded(const DisplayItem& displayItem, size_t index, DisplayItemIndicesByClientMap& displayItemIndicesByClient)
{
    if (!displayItem.isCacheable())
        return;

    DisplayItemIndicesByClientMap::iterator it = displayItemIndicesByClient.find(displayItem.client());
    Vector<size_t>& indices = it == displayItemIndicesByClient.end() ?
        displayItemIndicesByClient.add(displayItem.client(), Vector<size_t>()).storedValue->value : it->value;
    indices.append(index);
}
