Magnifier: Prevent useless operation in enabling/disabling magnifier.

On login, although the magnifier is disabled, the manager/controller try to disable it again. This CL prevents this useless operation.

Changes:
- In MagnificationManager::SetMagnifier(), if the given type is same as the current type, do nothing.
- In MagnificationControllerImpl::SetEnabled(), if the given |enabled| is same as current, do nothing.
- Use Initialize/Shutdown pattern instead of scoped_ptr in ChromeBrowserMainPartsChromeos.
- Initialize in PreProfileInit() instead of PostProfileInit().
- Add MagnificationObserver, and use it instead of watching pref changes.
- GetMagnifierType() returns the cached value.

BUG=163941
TEST=manual, browser_tests passes

Review URL: https://codereview.chromium.org/11280287

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171401 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 3 insertions, 0 deletions

diff --git a/ash/magnifier/magnification_controller.cc b/ash/magnifier/magnification_controller.cc
index d2169b3..1cbc56a 100644
--- a/ash/magnifier/magnification_controller.cc
+++ b/ash/magnifier/magnification_controller.cc
@@ -472,6 +472,9 @@ void MagnificationControllerImpl::EnsurePointIsVisible(
 }
 
 void MagnificationControllerImpl::SetEnabled(bool enabled) {
+  if (enabled == is_enabled_)
+    return;
+
   if (enabled) {
     float scale =
         ash::Shell::GetInstance()->delegate()->GetSavedScreenMagnifierScale();