Add setting to isolate zoom changes by default.

chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.cc

Index: chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.cc
diff --git a/chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.cc b/chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.cc
index 5092f549385ea777a8539c81655e69ca9ad97bf5..65accc23abfd23f34831b25459f18c0bb08c8cf8 100644
--- a/chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.cc
+++ b/chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.cc
@@ -5,15 +5,57 @@
 #include "chrome/browser/ui/zoom/chrome_zoom_level_otr_delegate.h"
 
 #include "base/bind.h"
+#include "chrome/common/pref_names.h"
 #include "components/zoom/zoom_event_manager.h"
 
 ChromeZoomLevelOTRDelegate::ChromeZoomLevelOTRDelegate(
+    PrefService* pref_service,
+    const base::FilePath& profile_path,
+    const base::FilePath& partition_path,
     base::WeakPtr<zoom::ZoomEventManager> zoom_event_manager)
-    : zoom_event_manager_(zoom_event_manager), host_zoom_map_(nullptr) {}
+    : partitioned_prefs_(pref_service, profile_path, partition_path),
+      zoom_event_manager_(zoom_event_manager),
+      host_zoom_map_(nullptr) {
+  // Observe changes to the zoom scope preference in case it is changed in the
+  // parent profile.
+  last_scope_was_per_origin_ = GetZoomScopeIsPerOriginPref();
+  pref_registrar_.Init(pref_service);
+  pref_registrar_.Add(
+      prefs::kPartitionZoomScopeIsPerOrigin,
+      base::Bind(&ChromeZoomLevelOTRDelegate::OnParentScopeChanged,
+                 base::Unretained(this)));
+}
 
 ChromeZoomLevelOTRDelegate::~ChromeZoomLevelOTRDelegate() {
 }
 
+bool ChromeZoomLevelOTRDelegate::GetZoomScopeIsPerOriginPref() const {
+  bool is_per_origin = kZoomScopeSettingDefault;
+
+  // If no value has been previously set, |is_per_origin| will be untouched
+  // from the default value we've set above.
+  partitioned_prefs_.GetBoolean(prefs::kPartitionZoomScopeIsPerOrigin,
+                                &is_per_origin);
+  return is_per_origin;
+}
+
+std::unique_ptr<ChromeZoomLevelOTRDelegate::DefaultZoomScopeSubscription>
+ChromeZoomLevelOTRDelegate::RegisterDefaultZoomScopeCallback(
+    const base::Closure& callback) {
+  return default_scope_changed_callbacks_.Add(callback);
+}
+
+void ChromeZoomLevelOTRDelegate::OnParentScopeChanged() {
+  bool new_scope_is_per_origin = GetZoomScopeIsPerOriginPref();
+  // Make sure that we're not being notified for a scope change in another
+  // partition.
+  if (new_scope_is_per_origin == last_scope_was_per_origin_)
+    return;
+
+  last_scope_was_per_origin_ = new_scope_is_per_origin;
+  default_scope_changed_callbacks_.Notify();
+}
+
 void ChromeZoomLevelOTRDelegate::InitHostZoomMap(
     content::HostZoomMap* host_zoom_map) {
   // This init function must be called only once.