Changes to sync/api/attachment in prep for integrating with sync API.

Make Attachment CopyAssignable so it can be used in STL containers.

Add some typedefs lists and maps of Attachments and AttachmentIds.

Make AttachmentStore::Write responsible for assigning/obtaining an
AttachmentId. This eliminates that case where a caller of
AttachmentStore can attempt to overwrite an existing attachment.

BUG=348624

Review URL: https://codereview.chromium.org/186633006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256269 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256269
Move ShouldClose from RenderViewHost to RenderFrameHost.

Renamed functions from ShouldClose to BeforeUnload to improve
consistency and reflect that it's not always for a close event.

Removes stale RendererManagement interface.

BUG=304341
TEST=No behavior change.

Review URL: https://codereview.chromium.org/189103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256270 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256270