Correct Javadoc build problems

Javadoc requires using HTML entities for certain characters, or else
they result in build errors.

Change-Id: Ie2f3b4b7636d07d95a8828a05401389fb718840f

gerrit-server/src/main/java/com/google/gerrit/metrics/CallbackMetric0.java

@@ -18,8 +18,8 @@ package com.google.gerrit.metrics;
  * Metric whose value is supplied when the trigger is invoked.
  *
  * <pre>
- *   CallbackMetric0<Long> hits = metricMaker.newCallbackMetric("hits", ...);
- *   CallbackMetric0<Long> total = metricMaker.newCallbackMetric("total", ...);
+ *   CallbackMetric0&lt;Long&gt; hits = metricMaker.newCallbackMetric("hits", ...);
+ *   CallbackMetric0&lt;Long&gt; total = metricMaker.newCallbackMetric("total", ...);
  *   metricMaker.newTrigger(hits, total, new Runnable() {
  *     public void run() {
  *       hits.set(1);

gerrit-server/src/main/java/com/google/gerrit/metrics/Counter0.java

@@ -35,7 +35,7 @@ public abstract class Counter0 implements RegistrationHandle {
   /**
    * Increment the counter by a specified amount.
    *
-   * @param value value to increment by, must be >= 0.
+   * @param value value to increment by, must be >= 0.
    */
   public abstract void incrementBy(long value);
 }

gerrit-server/src/main/java/com/google/gerrit/metrics/Counter1.java

@@ -38,7 +38,7 @@ public abstract class Counter1<F1> implements RegistrationHandle {
    * Increment the counter by a specified amount.
    *
    * @param field1 bucket to increment.
-   * @param value value to increment by, must be >= 0.
+   * @param value value to increment by, must be &gt;= 0.
    */
   public abstract void incrementBy(F1 field1, long value);
 }

gerrit-server/src/main/java/com/google/gerrit/metrics/Counter2.java

@@ -40,7 +40,7 @@ public abstract class Counter2<F1, F2> implements RegistrationHandle {
    *
    * @param field1 bucket to increment.
    * @param field2 bucket to increment.
-   * @param value value to increment by, must be >= 0.
+   * @param value value to increment by, must be &gt;= 0.
    */
   public abstract void incrementBy(F1 field1, F2 field2, long value);
 }

gerrit-server/src/main/java/com/google/gerrit/metrics/Counter3.java

@@ -42,7 +42,7 @@ public abstract class Counter3<F1, F2, F3> implements RegistrationHandle {
    * @param field1 bucket to increment.
    * @param field2 bucket to increment.
    * @param field3 bucket to increment.
-   * @param value value to increment by, must be >= 0.
+   * @param value value to increment by, must be &gt;= 0.
    */
   public abstract void incrementBy(F1 field1, F2 field2, F3 field3, long value);
 }