Remove all but one use of WeakPtrFactory::DetachFromThread

Remove all but one use of WeakPtrFactory::DetachFromThread. 

This is a re-land of issue 14299011, which broke GLSurfaceGLX, in turn breaking Chrome Linux/Aura.

This CL changes WeakPtr in the following ways: 
* Changes thread-bindings semantics so that WeakPtrs only become bound when the first one is dereferenced, or the owning factory invalidates them. 
* Removes WeakPtrFactory::DetachFromThread. 
* Renames SupportsWeakPtr::DetachFromThread to DetachFromThreadHack.

Calling code changes to allow this: 
* Unnecessary use of SupportsWeakPtr removed from SGIVideoSyncProviderThreadShim.
* Unnecessary DetachFromThread() calls removed from PluginInfoMessageFilter, DhcpProxyScript[Adapter]FetcherWin and (Chromoting's) PolicyWatcherLinux.
* DetachFromThread() calls rendered unnecessary by change in binding semantics removed from IOThread, SearchProviderInstallData, RuleRegistryWithCache and GLSurfaceGlx. 

WebGraphicsContext3DInProcessCommandBufferImpl uses the re-named DetachFromThreadHack() - bug 234964 tracks work to remove that use. 

TBR=darin,awong
BUG=232143, 234964, 243914
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=202811

[Wez, 2013-05-29 02:19:53]

FYI - original CL broke SGIVideoSyncProviderThreadShim's use of WeakPtr, which
wasn't necessary anyway, since the object's lifetime was managed by its only
caller. I've removed the unnecessary use of WeakPtr.

[commit-bot: I haz the power, 2013-05-29 02:20:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wez@chromium.org/16007009/2001

[darin (slow to review), 2013-05-29 04:35:06]

LGTM

[commit-bot: I haz the power, 2013-05-29 08:04:35]

Change committed as 202811