Rewrite Java histograms API implementation.

base/android/java/src/org/chromium/base/metrics/RecordHistogram.java

Index: base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
diff --git a/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java b/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
index 0ceddcd3ace2a255fce60b8687af2973fa9338ee..66c1ef0e4d920ce55c95fc272afb61d1b9cee685 100644
--- a/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
+++ b/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
@@ -7,6 +7,9 @@ package org.chromium.base.metrics;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.annotations.JNINamespace;
 
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -19,6 +22,8 @@ import java.util.concurrent.TimeUnit;
 @JNINamespace("base::android")
 public class RecordHistogram {
     private static boolean sIsDisabledForTests = false;
+    private static Map<String, Long> sCache =
+            Collections.synchronizedMap(new HashMap<String, Long>());
 
     /**
      * Tests may not have native initialized, so they may need to disable metrics.
@@ -28,6 +33,11 @@ public class RecordHistogram {
         sIsDisabledForTests = true;
     }
 
+    private static long getCachedHistogramKey(String name) {

[nyquist, 2016/04/01 21:37:14]

Could you add a short comment about what returning 0 entails and how native
reacts to that here?

[Alexei Svitkine (slow), 2016/04/04 15:08:09]

Done.

+        Long key = sCache.get(name);
+        return (key != null ? key : 0);

[nyquist, 2016/04/01 21:37:14]

Nit: I personally think it reads better to use == instead of !=.

[Alexei Svitkine (slow), 2016/04/04 15:08:09]

Done.

+    }
+
     /**
      * Records a sample in a boolean UMA histogram of the given name. Boolean histogram has two
      * buckets, corresponding to success (true) and failure (false). This is the Java equivalent of
@@ -37,7 +47,9 @@ public class RecordHistogram {
      */
     public static void recordBooleanHistogram(String name, boolean sample) {
         if (sIsDisabledForTests) return;
-        nativeRecordBooleanHistogram(name, System.identityHashCode(name), sample);
+        long key = getCachedHistogramKey(name);
+        long result = nativeRecordBooleanHistogram(name, key, sample);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -51,7 +63,9 @@ public class RecordHistogram {
      */
     public static void recordEnumeratedHistogram(String name, int sample, int boundary) {
         if (sIsDisabledForTests) return;
-        nativeRecordEnumeratedHistogram(name, System.identityHashCode(name), sample, boundary);
+        long key = getCachedHistogramKey(name);
+        long result = nativeRecordEnumeratedHistogram(name, key, sample, boundary);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -96,8 +110,9 @@ public class RecordHistogram {
     public static void recordCustomCountHistogram(
             String name, int sample, int min, int max, int numBuckets) {
         if (sIsDisabledForTests) return;
-        nativeRecordCustomCountHistogram(
-                name, System.identityHashCode(name), sample, min, max, numBuckets);
+        long key = getCachedHistogramKey(name);
+        long result = nativeRecordCustomCountHistogram(name, key, sample, min, max, numBuckets);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -112,8 +127,9 @@ public class RecordHistogram {
     public static void recordLinearCountHistogram(
             String name, int sample, int min, int max, int numBuckets) {
         if (sIsDisabledForTests) return;
-        nativeRecordLinearCountHistogram(
-                name, System.identityHashCode(name), sample, min, max, numBuckets);
+        long key = getCachedHistogramKey(name);
+        long result = nativeRecordLinearCountHistogram(name, key, sample, min, max, numBuckets);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -124,7 +140,9 @@ public class RecordHistogram {
      */
     public static void recordPercentageHistogram(String name, int sample) {
         if (sIsDisabledForTests) return;
-        nativeRecordEnumeratedHistogram(name, System.identityHashCode(name), sample, 101);
+        long key = getCachedHistogramKey(name);
+        long result = nativeRecordEnumeratedHistogram(name, key, sample, 101);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -135,7 +153,9 @@ public class RecordHistogram {
     */
     public static void recordSparseSlowlyHistogram(String name, int sample) {
         if (sIsDisabledForTests) return;
-        nativeRecordSparseHistogram(name, System.identityHashCode(name), sample);
+        long key = getCachedHistogramKey(name);
+        long result = nativeRecordSparseHistogram(name, key, sample);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -201,12 +221,14 @@ public class RecordHistogram {
     private static void recordCustomTimesHistogramMilliseconds(
             String name, long duration, long min, long max, int numBuckets) {
         if (sIsDisabledForTests) return;
+        long key = getCachedHistogramKey(name);
         // Note: Duration, min and max are clamped to int here because that's what's expected by
         // the native histograms API. Callers of these functions still pass longs because that's
         // the types returned by TimeUnit and System.currentTimeMillis() APIs, from which these
         // values come.
-        nativeRecordCustomTimesHistogramMilliseconds(name, System.identityHashCode(name),
-                clampToInt(duration), clampToInt(min), clampToInt(max), numBuckets);
+        long result = nativeRecordCustomTimesHistogramMilliseconds(
+                name, key, clampToInt(duration), clampToInt(min), clampToInt(max), numBuckets);
+        if (result != key) sCache.put(name, result);
     }
 
     /**
@@ -227,17 +249,17 @@ public class RecordHistogram {
         nativeInitialize();
     }
 
-    private static native void nativeRecordCustomTimesHistogramMilliseconds(
-            String name, int key, int duration, int min, int max, int numBuckets);
+    private static native long nativeRecordCustomTimesHistogramMilliseconds(
+            String name, long key, int duration, int min, int max, int numBuckets);
 
-    private static native void nativeRecordBooleanHistogram(String name, int key, boolean sample);
-    private static native void nativeRecordEnumeratedHistogram(
-            String name, int key, int sample, int boundary);
-    private static native void nativeRecordCustomCountHistogram(
-            String name, int key, int sample, int min, int max, int numBuckets);
-    private static native void nativeRecordLinearCountHistogram(
-            String name, int key, int sample, int min, int max, int numBuckets);
-    private static native void nativeRecordSparseHistogram(String name, int key, int sample);
+    private static native long nativeRecordBooleanHistogram(String name, long key, boolean sample);
+    private static native long nativeRecordEnumeratedHistogram(
+            String name, long key, int sample, int boundary);
+    private static native long nativeRecordCustomCountHistogram(
+            String name, long key, int sample, int min, int max, int numBuckets);
+    private static native long nativeRecordLinearCountHistogram(
+            String name, long key, int sample, int min, int max, int numBuckets);
+    private static native long nativeRecordSparseHistogram(String name, long key, int sample);
 
     private static native int nativeGetHistogramValueCountForTesting(String name, int sample);
     private static native void nativeInitialize();