Revert 176340

Revert 176340
> sync: Initialize entries with a valid model type
> 
> This change modifies two important sync functions.
> 
> The first is MutableEntry's CREATE constructor.  It now requires that
> the ModelType of the entry to be specified when the entry is create.
> This doesn't quite eliminate the existence of nodes without a valid
> model type (the CREATE_NEW_UPDATE_ITEM can still make them), but it
> helps.
> 
> This paves the way for the upcoming UniquePosition change.  Part of that
> change is that bookmarks must be granted a unique tag on creation.  To
> support this, we must know at creation time the type of a new entry, so
> we can take the appropriate bookmark-specific steps if necessary.
> 
> The second function to get a new signature is WriteNode's
> InitByCreation(), which has been renamed to
> WriteNode::InitBookmarkByCreation().  The function can only be used to
> create bookmarks, so the new name describes its function more precisely.
> 
> Updates to the call-sites of MutableEntry's constructor make up the
> majority of this change.  This change also includes some minor updates
> to test functions that create entries to make them compatible with the
> stricter assertions or to make them more closely reflect real world
> behaviour.
> 
> BUG=145412, 126505
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/11817010

TBR=rlarocque@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=176352