Revert of Introduce HostID and de-couple Extensions from "script injection System" [browser side]

Revert of Introduce HostID and de-couple Extensions from "script injection System" [browser side] (patchset #20 id:760001 of https://codereview.chromium.org/822453002/)

Reason for revert:
It might cause the crash https://code.google.com/p/chromium/issues/detail?id=454917.

Original issue's description:
> Introduce HostID and de-couple Extensions from "script injection System" [browser side]
>
> The major refactor includes:
> - Introduce HostID (a pair of |id, type|) to replace extension_id in browser
>   side.
> - Abstract UserScriptLoader to be a base class, and introduces
>   a derived class ExtensionUserScriptLoader which is
>   responsible for loading user scripts for extensions.
> - In DeclarativeUserScriptManager, a master is created per
>   extension/webUI.
> - DeclarativeUserScriptManager becomes an
>   ExtensionRegistryObserver and is responsible for clearing scripts
>   for master objects when receive OnExensionUnloaded event.
>
> BUG=437566
>
> Committed: https://crrev.com/b88fe3dc1072501bdd105fd95a8b3bc453fd2aa7
> Cr-Commit-Position: refs/heads/master@{#313402}

TBR=fsamuel@chromium.org,rdevlin.cronin@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=437566
Committed: https://crrev.com/5eb894ea21637241e9a78fb9c2737d40d6dbf575
Cr-Commit-Position: refs/heads/master@{#314631}

[Xi Han, 2015-02-04 20:41:25]

Created Revert of Introduce HostID and de-couple Extensions from "script
injection System" [browser side]

[commit-bot: I haz the power, 2015-02-04 20:42:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/899983002/1

[commit-bot: I haz the power, 2015-02-04 20:43:32]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-02-04 20:43:33]

Failed to apply patch for extensions/common/BUILD.gn:
While running git apply --index -3 -p1;
  error: patch failed: extensions/common/BUILD.gn:109
  Falling back to three-way merge...
  Applied patch to 'extensions/common/BUILD.gn' with conflicts.
  U extensions/common/BUILD.gn

Patch:       extensions/common/BUILD.gn
Index: extensions/common/BUILD.gn
diff --git a/extensions/common/BUILD.gn b/extensions/common/BUILD.gn
index
ebfd09daed4407540189d33fbb4801b93f71d666..c23df445dac06ee88d0676551000d9ef07c768c0
100644
--- a/extensions/common/BUILD.gn
+++ b/extensions/common/BUILD.gn
@@ -109,7 +109,6 @@
       "file_util.h",
       "guest_view/guest_view_constants.cc",
       "guest_view/guest_view_constants.h",
-      "host_id.h",
       "image_util.cc",
       "image_util.h",
       "install_warning.cc",

[commit-bot: I haz the power, 2015-02-04 20:43:47]

The CQ bit was unchecked by commit-bot@chromium.org

[Xi Han, 2015-02-04 21:03:39]

The CQ bit was checked by hanxi@chromium.org

[commit-bot: I haz the power, 2015-02-04 21:04:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/899983002/270001

[commit-bot: I haz the power, 2015-02-04 21:06:08]

Committed patchset #2 (id:270001)

[commit-bot: I haz the power, 2015-02-04 21:07:12]

Patchset 2 (id:??) landed as
https://crrev.com/5eb894ea21637241e9a78fb9c2737d40d6dbf575
Cr-Commit-Position: refs/heads/master@{#314631}

[Xi Han, 2015-02-05 14:22:03]

A revert of this CL (patchset #2 id:270001) has been created in
https://codereview.chromium.org/903743002/ by hanxi@chromium.org.

The reason for reverting is: It turns out that the crash wasn't caused by this
CL..