[InputEvent] Add 'beforeinput' logic in |will*()| and guarded by a flag (3/11)

third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h

Index: third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
diff --git a/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h b/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
index 4419c21e0586beaa45d16d51f42e2cc19dcc7dd4..42e7a84b88531075f168f80ac3ebba21b90e3a3f 100644
--- a/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
+++ b/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
@@ -80,8 +80,8 @@ class EditCommandComposition final : public UndoStep {
                          const VisibleSelection& startingSelection,
                          const VisibleSelection& endingSelection);
 
-  // TODO(chongz): Implement "beforeinput" as described below:
-  // Fires "beforeinput" and will returns |false| to cancel unapply / reapply if
+  // Fires "beforeinput" if |BeforeInputTiming == kShouldFireInCommand|.
+  // Will return |false| to cancel unapply / reapply if
   //   * "beforeinput" was canceled, or
   //   * |frame| was destroyed by event handlers.
   // Note: Undo stack will always get popped.
@@ -133,8 +133,8 @@ class CORE_EXPORT CompositeEditCommand : public EditCommand {
  protected:
   explicit CompositeEditCommand(Document&);
 
-  // TODO(chongz): Implement "beforeinput" as described below:
-  // Fires "beforeinput" and will return |false| to cancel applying editing if
+  // Fires "beforeinput" if |BeforeInputTiming == kShouldFireInCommand|.
+  // Will return |false| to cancel applying editing if
   //   * "beforeinput" was canceled, or
   //   * |frame| was destroyed by event handlers.
   // |willApplyEditing()| should be called from