Bug 1051556 - Make GeckoEditable.onTextChange more efficient; r=esawin

This patch simplifies the onTextChange method, makes it more efficient
by avoiding unnecessary text copying, and fixes some small bugs.

mobile/android/base/java/org/mozilla/gecko/GeckoEditable.java

@@ -968,10 +968,14 @@ final class GeckoEditable extends JNIObject
     }
 
     private void geckoReplaceText(int start, int oldEnd, CharSequence newText) {
+        if (AppConstants.Versions.preHC) {
             // Don't use replace() because Gingerbread has a bug where if the replaced text
             // has the same spans as the original text, the spans will end up being deleted
             mText.delete(start, oldEnd);
             mText.insert(start, newText);
+        } else {
+            mText.replace(start, oldEnd, newText);
+        }
     }
 
     private boolean isSameText(int start, int oldEnd, CharSequence newText) {
@@ -1013,44 +1017,24 @@ final class GeckoEditable extends JNIObject
             // Simply replace the text for newly-focused editors.
             mText.replace(0, mText.length(), text);
 
-        } else {
-            mChangedText.clearSpans();
-            mChangedText.replace(0, mChangedText.length(), text);
-            // Preserve as many spans as possible
-            TextUtils.copySpansFrom(mText, start, Math.min(oldEnd, newEnd),
-                                    Object.class, mChangedText, 0);
-
-            if (action != null &&
+        } else if (action != null &&
                 action.mType == Action.TYPE_REPLACE_TEXT &&
                 start <= action.mStart &&
-                    action.mStart + action.mSequence.length() <= newEnd) {
+                oldEnd >= action.mEnd &&
+                newEnd >= action.mStart + action.mSequence.length()) {
 
             // actionNewEnd is the new end of the original replacement action
             final int actionNewEnd = action.mStart + action.mSequence.length();
-                int selStart = Selection.getSelectionStart(mText);
-                int selEnd = Selection.getSelectionEnd(mText);
 
             // Replace old spans with new spans
-                mChangedText.replace(action.mStart - start, actionNewEnd - start,
-                                     action.mSequence);
+            if (start == action.mStart && oldEnd == action.mEnd && newEnd == actionNewEnd) {
+                // The new text exactly matches our sequence, so do a direct replace.
+                geckoReplaceText(start, oldEnd, action.mSequence);
+            } else {
+                mChangedText.clearSpans();
+                mChangedText.replace(0, mChangedText.length(), mText, start, oldEnd);
+                mChangedText.replace(action.mStart - start, action.mEnd - start, action.mSequence);
                 geckoReplaceText(start, oldEnd, mChangedText);
-
-                // delete/insert above might have moved our selection to somewhere else
-                // this happens when the Gecko text change covers a larger range than
-                // the original replacement action. Fix selection here
-                if (selStart >= start && selStart <= oldEnd) {
-                    selStart = selStart < action.mStart ? selStart :
-                               selStart < action.mEnd   ? actionNewEnd :
-                                                          selStart + actionNewEnd - action.mEnd;
-                    mText.setSpan(Selection.SELECTION_START, selStart, selStart,
-                                  Spanned.SPAN_POINT_POINT);
-                }
-                if (selEnd >= start && selEnd <= oldEnd) {
-                    selEnd = selEnd < action.mStart ? selEnd :
-                             selEnd < action.mEnd   ? actionNewEnd :
-                                                      selEnd + actionNewEnd - action.mEnd;
-                    mText.setSpan(Selection.SELECTION_END, selEnd, selEnd,
-                                  Spanned.SPAN_POINT_POINT);
             }
 
             // Ignore the next selection change because the selection change is a
@@ -1059,7 +1043,7 @@ final class GeckoEditable extends JNIObject
 
         } else {
             // Gecko side initiated the text change.
-                if (isSameText(start, oldEnd, mChangedText)) {
+            if (isSameText(start, oldEnd, text)) {
                 // Nothing to do because the text is the same. This could happen when
                 // the composition is updated for example. Ignore the next selection
                 // change because the selection change is a side-effect of the
@@ -1067,8 +1051,8 @@ final class GeckoEditable extends JNIObject
                 mIgnoreSelectionChange = true;
                 return;
             }
-                geckoReplaceText(start, oldEnd, mChangedText);
-            }
+
+            geckoReplaceText(start, oldEnd, text);
         }
 
         geckoPostToIc(new Runnable() {