Bug 1176954 part.5 IMENotification::TextChangeDataBase should have a state which indicates that it's not initialized r=smaug

widget/android/nsWindow.cpp

@@ -1737,6 +1737,7 @@ nsWindow::OnIMEEvent(AndroidGeckoEvent *ae)
             // combine with this text change, and overflow might occur if
             // we just use INT32_MAX
             IMENotification notification(NOTIFY_IME_OF_TEXT_CHANGE);
+            notification.mTextChangeData.mStartOffset = 0;
             notification.mTextChangeData.mRemovedEndOffset =
                 notification.mTextChangeData.mAddedEndOffset = INT32_MAX / 2;
             NotifyIMEOfTextChange(notification);

widget/android/nsWindow.h

@@ -189,6 +189,8 @@ protected:
             MOZ_ASSERT(aIMENotification.mMessage ==
                            mozilla::widget::NOTIFY_IME_OF_TEXT_CHANGE,
                        "IMEChange initialized with wrong notification");
+            MOZ_ASSERT(aIMENotification.mTextChangeData.IsValid(),
+                       "The text change notification isn't initialized");
             MOZ_ASSERT(aIMENotification.mTextChangeData.IsInInt32Range(),
                        "The text change notification is out of range");
         }

widget/nsIWidget.h

@@ -616,10 +616,7 @@ struct IMENotification
         mSelectionChangeData.mCausedByComposition = false;
         break;
       case NOTIFY_IME_OF_TEXT_CHANGE:
-        mTextChangeData.mStartOffset = 0;
-        mTextChangeData.mRemovedEndOffset = 0;
-        mTextChangeData.mAddedEndOffset = 0;
-        mTextChangeData.mCausedByComposition = false;
+        mTextChangeData.Clear();
         break;
       case NOTIFY_IME_OF_MOUSE_BUTTON_EVENT:
         mMouseButtonEventData.mEventMessage = 0;
@@ -734,15 +731,36 @@ struct IMENotification
 
     bool mCausedByComposition;
 
-    uint32_t OldLength() const { return mRemovedEndOffset - mStartOffset; }
-    uint32_t NewLength() const { return mAddedEndOffset - mStartOffset; }
+    uint32_t OldLength() const
+    {
+      MOZ_ASSERT(IsValid());
+      return mRemovedEndOffset - mStartOffset;
+    }
+    uint32_t NewLength() const
+    {
+      MOZ_ASSERT(IsValid());
+      return mAddedEndOffset - mStartOffset;
+    }
 
     bool IsInInt32Range() const
     {
+      MOZ_ASSERT(IsValid());
       return mStartOffset <= INT32_MAX &&
              mRemovedEndOffset <= INT32_MAX &&
              mAddedEndOffset <= INT32_MAX;
     }
+
+    bool IsValid() const
+    {
+      return !(mStartOffset == UINT32_MAX &&
+               !mRemovedEndOffset && !mAddedEndOffset);
+    }
+
+    void Clear()
+    {
+      mStartOffset = UINT32_MAX;
+      mRemovedEndOffset = mAddedEndOffset = 0;
+    }
   };
 
   union