Migrate BandwidthType to @IntDef

@IntDef/@StringDef annotation are preferred way for declaring
set of String/int values.

1. they need less space in APK than enum, see
https://developer.android.com/topic/performance/reduce-apk-size#remove-enums
2. they give more control over allowed values than "static final" values

Main goal of patch is writing "static final" values, enum
and some classes in one common @IntDef/@StringDef form:

1. with @IntDef/@StringDef first, @Retention second
   and related @interface third
2. with values inside @interface
3. with NUM_ENTRIES declaring number of entries if necessary
4. with comment about numbering from 0 without gaps when necessary
5. with @Retention(RetentionPolicy.SOURCE)
6. without "static final" in the @interface

Change-Id: I4cc6bde5c2d738bf5bc908735110ac420325e86c
Reviewed-on: https://chromium-review.googlesource.com/1183663Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Marcin Wiącek <marcin@mwiacek.com>
Cr-Commit-Position: refs/heads/master@{#585551}

chrome/android/java/src/org/chromium/chrome/browser/preferences/privacy/BandwidthType.java

@@ -4,31 +4,34 @@
 
 package org.chromium.chrome.browser.preferences.privacy;
 
+import android.support.annotation.IntDef;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
 /**
  * Bandwidth options available based on network.
  */
-public enum BandwidthType {
-
-    // Still using "prerender" in the strings for historical reasons: we don't want to break
-    // existing users' settings.
-    NEVER_PRERENDER      ("never_prefetch"),
-    PRERENDER_ON_WIFI    ("prefetch_on_wifi"),
-    ALWAYS_PRERENDER     ("always_prefetch");
-
-    public static final BandwidthType DEFAULT = PRERENDER_ON_WIFI;
-
-    private final String mTitle;
-
-    BandwidthType(String title) {
-        mTitle = title;
+public class BandwidthType {
+    @IntDef({Type.NEVER_PRERENDER, Type.PRERENDER_ON_WIFI, Type.ALWAYS_PRERENDER})
+    @Retention(RetentionPolicy.SOURCE)
+    public @interface Type {
+        // Values are numbered from 0 and can't have gaps.
+        int NEVER_PRERENDER = 0;
+        int PRERENDER_ON_WIFI = 1; // Default option.
+        int ALWAYS_PRERENDER = 2;
+        int NUM_ENTRIES = 3;
     }
 
+    private final static String[] TITLES = {
+            "never_prefetch", "prefetch_on_wifi", "always_prefetch"};
+
     /**
      * Returns the title of the bandwidthType.
      * @return title
      */
-    public String title() {
-        return mTitle;
+    public static String title(@Type int type) {
+        return TITLES[type];
     }
 
     /**
@@ -36,11 +39,11 @@ public enum BandwidthType {
      * @param title
      * @return BandwidthType
      */
-    public static BandwidthType getBandwidthFromTitle(String title) {
-        for (BandwidthType b : BandwidthType.values()) {
-            if (b.mTitle.equals(title)) return b;
+    public static @BandwidthType.Type int getBandwidthFromTitle(String title) {
+        for (@BandwidthType.Type int i = Type.NEVER_PRERENDER; i < Type.NUM_ENTRIES; i++) {
+            if (TITLES[i].equals(title)) return i;
         }
         assert false;
-        return DEFAULT;
+        return Type.PRERENDER_ON_WIFI;
     }
 }

chrome/android/java/src/org/chromium/chrome/browser/preferences/privacy/PrivacyPreferencesManager.java

@@ -178,7 +178,8 @@ public class PrivacyPreferencesManager implements CrashReportingPermissionManage
         // Migrate if the old preferences are at their default values.
         // (Note that for PREF_BANDWIDTH*, if the setting is default, then there is no way to tell
         // whether the user has set it.)
-        final String prefBandwidthDefault = BandwidthType.PRERENDER_ON_WIFI.title();
+        final String prefBandwidthDefault =
+                BandwidthType.title(BandwidthType.Type.PRERENDER_ON_WIFI);
         final String prefBandwidth =
                 mSharedPreferences.getString(PREF_BANDWIDTH_OLD, prefBandwidthDefault);
         boolean prefBandwidthNoCellularDefault = true;
@@ -191,12 +192,13 @@ public class PrivacyPreferencesManager implements CrashReportingPermissionManage
             // Observe PREF_BANDWIDTH on mobile network capable devices.
             if (isMobileNetworkCapable()) {
                 if (mSharedPreferences.contains(PREF_BANDWIDTH_OLD)) {
-                    BandwidthType prefetchBandwidthTypePref = BandwidthType.getBandwidthFromTitle(
-                            prefBandwidth);
-                    if (BandwidthType.NEVER_PRERENDER.equals(prefetchBandwidthTypePref)) {
+                    @BandwidthType.Type
+                    int prefetchBandwidthTypePref =
+                            BandwidthType.getBandwidthFromTitle(prefBandwidth);
+                    if (BandwidthType.Type.NEVER_PRERENDER == prefetchBandwidthTypePref) {
                         newValue = false;
-                    } else if (BandwidthType.PRERENDER_ON_WIFI.equals(prefetchBandwidthTypePref)
-                            || BandwidthType.ALWAYS_PRERENDER.equals(prefetchBandwidthTypePref)) {
+                    } else if (BandwidthType.Type.PRERENDER_ON_WIFI == prefetchBandwidthTypePref
+                            || BandwidthType.Type.ALWAYS_PRERENDER == prefetchBandwidthTypePref) {
                         newValue = true;
                     }
                 }