Add setting for configuring zoom level on double-tap.

Added a seek bar in Accessibility settings to configure the zoom level
on double-tap. The range is 75-125% with the default of 100% equal to
the display density.

Bug: 5312461
Change-Id: Iaf1b9f6f6659146db4031c5f819ef9cb55695b5c
diff --git a/res/xml/accessibility_preferences.xml b/res/xml/accessibility_preferences.xml
index ac96e6e..8eca917 100644
--- a/res/xml/accessibility_preferences.xml
+++ b/res/xml/accessibility_preferences.xml
@@ -33,6 +33,12 @@
             android:max="30" />
 
         <com.android.browser.preferences.SeekBarSummaryPreference
+            android:key="double_tap_zoom"
+            android:title="@string/pref_zoom_on_double_tap"
+            android:defaultValue="5"
+            android:max="10" />
+
+        <com.android.browser.preferences.SeekBarSummaryPreference
             android:key="min_font_size"
             android:title="@string/pref_min_font_size"
             android:defaultValue="0"