Add a finch flag to disable ContextualSearch selection expansion.

chrome/android/java/src/org/chromium/chrome/browser/contextualsearch/ContextualSearchSelectionController.java

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.contextualsearch;
 
 import android.os.Handler;
 
 import org.chromium.base.VisibleForTesting;
 import org.chromium.chrome.browser.ChromeActivity;
@@ skipping 276 matching lines @@
     }
 
     /**
      * Expands the current selection by the specified amounts.
      * @param selectionStartAdjust The start offset adjustment of the selection to use to highlight
      *                             the search term.
      * @param selectionEndAdjust The end offset adjustment of the selection to use to highlight
      *                           the search term.
      */
     void adjustSelection(int selectionStartAdjust, int selectionEndAdjust) {
+        if (ContextualSearchFieldTrial.isSelectionExpansionDisabled()) return;
+
         // TODO(donnd): add code to verify that the selection is still valid before changing it.
         // crbug.com/508354
 
         if (selectionStartAdjust == 0 && selectionEndAdjust == 0) return;
         ContentViewCore basePageContentView = getBaseContentView();
         if (basePageContentView != null && basePageContentView.getWebContents() != null) {
             mDidExpandSelection = true;
             basePageContentView.getWebContents().adjustSelectionByCharacterOffset(
                     selectionStartAdjust, selectionEndAdjust);
         }
@@ skipping 73 matching lines @@
     /**
      * Determines if the given selection contains a word or not.
      * @param selection The the selection to check for a word.
      * @return Whether the selection contains a word anywhere within it or not.
      */
     @VisibleForTesting
     public boolean doesContainAWord(String selection) {
         return mContainsWordPattern.matcher(selection).find();
     }
 }