Update gitignore and include TagMap[Builder].

.gitignore

@@ -35,6 +35,3 @@ bin
 
 # Vim
 .swp
-
-# Other
-TAGS

api/src/main/java/openconsensus/tags/TagMap.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2019, OpenConsensus Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package openconsensus.tags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A map from {@link TagKey} to {@link TagValue} that can be used to label anything that is
+ * associated with a specific operation.
+ *
+ * <p>For example, {@code TagMap}s can be used to label stats, log messages, or debugging
+ * information.
+ *
+ * @since 0.1.0
+ */
+@Immutable
+public abstract class TagMap {
+  @Override
+  public String toString() {
+    return "TagMap";
+  }
+}

api/src/main/java/openconsensus/tags/TagMapBuilder.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2019, OpenConsensus Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package openconsensus.tags;
+
+import openconsensus.common.Scope;
+
+/**
+ * Builder for the {@link TagMap} class.
+ *
+ * @since 0.1.0
+ */
+public abstract class TagMapBuilder {
+  /**
+   * Adds the key/value pair and metadata regardless of whether the key is present.
+   *
+   * @param key the {@code TagKey} which will be set.
+   * @param value the {@code TagValue} to set for the given key.
+   * @param tagMetadata the {@code TagMetadata} associated with this {@link Tag}.
+   * @return this
+   * @since 0.1.0
+   */
+  public abstract TagMapBuilder put(TagKey key, TagValue value, TagMetadata tagMetadata);
+
+  /**
+   * Removes the key if it exists.
+   *
+   * @param key the {@code TagKey} which will be removed.
+   * @return this
+   * @since 0.1.0
+   */
+  public abstract TagMapBuilder remove(TagKey key);
+
+  /**
+   * Creates a {@code TagMap} from this builder.
+   *
+   * @return a {@code TagMap} with the same tags as this builder.
+   * @since 0.1.0
+   */
+  public abstract TagMap build();
+
+  /**
+   * Enters the scope of code where the {@link TagMap} created from this builder is in the current
+   * context and returns an object that represents that scope. The scope is exited when the returned
+   * object is closed.
+   *
+   * @return an object that defines a scope where the {@code TagMap} created from this builder is
+   *     set to the current context.
+   * @since 0.1.0
+   */
+  public abstract Scope buildScoped();
+}