Updating sticky headers.

- The whole section's headers are drawn together, moving as a group
  until it reaches the individual bounds for each letter in the section
- Adding animation to search button -> field transition
- Fixing section header text measuring causing sections not to be centered
- Forcing the merge to stop if an app has > 3 full rows; on both phone and
  tablet, merging a large section with anything else seems to be less useful

src/com/android/launcher3/AppsContainerSearchEditTextView.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.launcher3;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.view.KeyEvent;
+import android.widget.EditText;
+
+
+/**
+ * The edit text for the search container
+ */
+public class AppsContainerSearchEditTextView extends EditText {
+
+    /**
+     * Implemented by listeners of the back key.
+     */
+    public interface OnBackKeyListener {
+        public void onBackKey();
+    }
+
+    private OnBackKeyListener mBackKeyListener;
+
+    public AppsContainerSearchEditTextView(Context context) {
+        this(context, null);
+    }
+
+    public AppsContainerSearchEditTextView(Context context, AttributeSet attrs) {
+        this(context, attrs, 0);
+    }
+
+    public AppsContainerSearchEditTextView(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+    }
+
+    public void setOnBackKeyListener(OnBackKeyListener listener) {
+        mBackKeyListener = listener;
+    }
+
+    @Override
+    public boolean onKeyPreIme(int keyCode, KeyEvent event) {
+        // If this is a back key, propagate the key back to the listener
+        if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_UP) {
+            if (mBackKeyListener != null) {
+                mBackKeyListener.onBackKey();
+            }
+            return false;
+        }
+        return super.onKeyPreIme(keyCode, event);
+    }
+}