Make SignalStrength#INVALID public

Bug: 113074174
Bug: 118460482
Test: Treehugger; compile
Change-Id: I088f2f46c0adfbedc0fd53838add57078d6aac56
diff --git a/api/current.txt b/api/current.txt
index 443116f..bd7c522 100755
--- a/api/current.txt
+++ b/api/current.txt
@@ -42467,6 +42467,7 @@
     method public int getLevel();
     method public boolean isGsm();
     method public void writeToParcel(android.os.Parcel, int);
+    field public static final int INVALID = 2147483647; // 0x7fffffff
   }
 
   public final class SmsManager {
diff --git a/telephony/java/android/telephony/SignalStrength.java b/telephony/java/android/telephony/SignalStrength.java
index fb801b2..def5e7d8 100644
--- a/telephony/java/android/telephony/SignalStrength.java
+++ b/telephony/java/android/telephony/SignalStrength.java
@@ -65,8 +65,9 @@
     };
 
     /**
-     * Use Integer.MAX_VALUE because -1 is a valid value in signal strength.
-     * @hide
+     * Indicates the invalid measures of signal strength.
+     *
+     * For example, this can be returned by {@link #getEvdoDbm()} or {@link #getCdmaDbm()}
      */
     public static final int INVALID = Integer.MAX_VALUE;
 
@@ -173,9 +174,9 @@
     public SignalStrength(boolean gsmFlag) {
         mGsmSignalStrength = 99;
         mGsmBitErrorRate = -1;
-        mCdmaDbm = -1;
+        mCdmaDbm = INVALID;
         mCdmaEcio = -1;
-        mEvdoDbm = -1;
+        mEvdoDbm = INVALID;
         mEvdoEcio = -1;
         mEvdoSnr = -1;
         mLteSignalStrength = 99;
@@ -542,6 +543,8 @@
 
     /**
      * Get the CDMA RSSI value in dBm
+     *
+     * @return the CDMA RSSI value or {@link #INVALID} if invalid
      */
     public int getCdmaDbm() {
         return this.mCdmaDbm;
@@ -556,6 +559,8 @@
 
     /**
      * Get the EVDO RSSI value in dBm
+     *
+     * @return the EVDO RSSI value or {@link #INVALID} if invalid
      */
     public int getEvdoDbm() {
         return this.mEvdoDbm;