Move ExtensionHost from src/chrome to src/extensions

This breaks another src/extensions -> src/chrome dependency.

* Mechanical file move.
* Clean up DEPS.
* Move pinch-to-zoom handling to ExtensionViewHost as it only applies to
  visible extension content.

No functional changes.

BUG=321341
TEST=browser_tests *Extension*
[email protected] for header file rename across chrome/browser

Review URL: https://codereview.chromium.org/198703006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@258494 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/alert_apitest.cc b/chrome/browser/extensions/alert_apitest.cc
index 0b8cc6bb..893a9b4 100644
--- a/chrome/browser/extensions/alert_apitest.cc
+++ b/chrome/browser/extensions/alert_apitest.cc
@@ -4,12 +4,12 @@
 
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/extensions/extension_apitest.h"
-#include "chrome/browser/extensions/extension_host.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/app_modal_dialogs/app_modal_dialog.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "content/public/browser/render_frame_host.h"
+#include "extensions/browser/extension_host.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/browser/process_manager.h"
 #include "extensions/common/extension.h"