Add the partial screen magnifier to Chrome OS.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 3584a2f4487f1004e0002fd77d5d4cefae019dbc..04a93b3895339abc983afcb35a7361f0acf6e7fa 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -23,6 +23,7 @@
 #include "ash/high_contrast/high_contrast_controller.h"
 #include "ash/launcher/launcher.h"
 #include "ash/magnifier/magnification_controller.h"
+#include "ash/magnifier/partial_magnification_controller.h"
 #include "ash/root_window_controller.h"
 #include "ash/screen_ash.h"
 #include "ash/shell_delegate.h"
@@ -246,6 +247,7 @@ Shell::~Shell() {
   // Alphabetical.
   drag_drop_controller_.reset();
   magnification_controller_.reset();
+  partial_magnification_controller_.reset();
   power_button_controller_.reset();
   resize_shadow_controller_.reset();
   shadow_controller_.reset();
@@ -443,6 +445,9 @@ void Shell::Init() {
   magnification_controller_.reset(
       internal::MagnificationController::CreateInstance());
 
+  partial_magnification_controller_.reset(
+      new internal::PartialMagnificationController());
+
   high_contrast_controller_.reset(new HighContrastController);
   video_detector_.reset(new VideoDetector);
   window_cycle_controller_.reset(