events: Introduce non-cancelable events.

A ui::Event can be canceled by default. But some events should not
be cancelable (e.g. focus-change events).

BUG=163617

Review URL: https://codereview.chromium.org/11443027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171851 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 21 insertions, 3 deletions

diff --git a/ui/base/events/event.cc b/ui/base/events/event.cc
index e6cbd25..317d93c 100644
--- a/ui/base/events/event.cc
+++ b/ui/base/events/event.cc
@@ -120,13 +120,18 @@ bool Event::HasNativeEvent() const {
 }
 
 void Event::StopPropagation() {
-//  CHECK(phase_ != EP_PREDISPATCH && phase_ != EP_POSTDISPATCH);
+  // TODO(sad): Re-enable these checks once View uses dispatcher to dispatch
+  // events.
+  // CHECK(phase_ != EP_PREDISPATCH && phase_ != EP_POSTDISPATCH);
+  CHECK(cancelable_);
   result_ = static_cast<ui::EventResult>(result_ | ER_CONSUMED);
-  CHECK(stopped_propagation());
 }
 
 void Event::SetHandled() {
-//  CHECK(phase_ != EP_PREDISPATCH && phase_ != EP_POSTDISPATCH);
+  // TODO(sad): Re-enable these checks once View uses dispatcher to dispatch
+  // events.
+  // CHECK(phase_ != EP_PREDISPATCH && phase_ != EP_POSTDISPATCH);
+  CHECK(cancelable_);
   result_ = static_cast<ui::EventResult>(result_ | ER_HANDLED);
 }
 
@@ -136,6 +141,7 @@ Event::Event(EventType type, base::TimeDelta time_stamp, int flags)
       flags_(flags),
       dispatch_to_hidden_targets_(false),
       delete_native_event_(false),
+      cancelable_(true),
       target_(NULL),
       phase_(EP_PREDISPATCH),
       result_(ER_UNHANDLED) {
@@ -152,6 +158,7 @@ Event::Event(const base::NativeEvent& native_event,
       flags_(flags),
       dispatch_to_hidden_targets_(false),
       delete_native_event_(false),
+      cancelable_(true),
       target_(NULL),
       phase_(EP_PREDISPATCH),
       result_(ER_UNHANDLED) {
@@ -167,6 +174,7 @@ Event::Event(const Event& copy)
       flags_(copy.flags_),
       dispatch_to_hidden_targets_(false),
       delete_native_event_(false),
+      cancelable_(true),
       target_(NULL),
       phase_(EP_PREDISPATCH),
       result_(ER_UNHANDLED) {
diff --git a/ui/base/events/event.h b/ui/base/events/event.h
index 2115402..4cdbd18 100644
--- a/ui/base/events/event.h
+++ b/ui/base/events/event.h
@@ -80,6 +80,12 @@ class UI_EXPORT Event {
     return dispatch_to_hidden_targets_;
   }
 
+  // By default, events are "cancelable", this means any default processing that
+  // the containing abstraction layer may perform can be prevented by calling
+  // SetHandled(). SetHandled() or StopPropagation() must not be called for
+  // events that are not cancelable.
+  bool cancelable() const { return cancelable_; }
+
   // The following methods return true if the respective keys were pressed at
   // the time the event was created.
   bool IsShiftDown() const { return (flags_ & EF_SHIFT_DOWN) != 0; }
@@ -168,6 +174,8 @@ class UI_EXPORT Event {
   // Immediately stops the propagation of the event. This must be called only
   // from an EventHandler during an event-dispatch. Any event handler that may
   // be in the list will not receive the event after this is called.
+  // Note that StopPropagation() or SetHandled() must not be called for
+  // cancelable events.
   void StopPropagation();
   bool stopped_propagation() const { return !!(result_ & ui::ER_CONSUMED); }
 
@@ -182,6 +190,7 @@ class UI_EXPORT Event {
   void set_delete_native_event(bool delete_native_event) {
     delete_native_event_ = delete_native_event;
   }
+  void set_cancelable(bool cancelable) { cancelable_ = cancelable; }
   void set_time_stamp(base::TimeDelta time_stamp) { time_stamp_ = time_stamp; }
   void set_dispatch_to_hidden_targets(bool dispatch_to_hidden_targets) {
     dispatch_to_hidden_targets_ = dispatch_to_hidden_targets;
@@ -203,6 +212,7 @@ class UI_EXPORT Event {
   int flags_;
   bool dispatch_to_hidden_targets_;
   bool delete_native_event_;
+  bool cancelable_;
   EventTarget* target_;
   EventPhase phase_;
   EventResult result_;