Export parameter default values to the proto file.

RELNOTES: None
PiperOrigin-RevId: 210369021
diff --git a/src/main/java/com/google/devtools/build/docgen/ApiExporter.java b/src/main/java/com/google/devtools/build/docgen/ApiExporter.java
index 3ca4b02..4091322 100644
--- a/src/main/java/com/google/devtools/build/docgen/ApiExporter.java
+++ b/src/main/java/com/google/devtools/build/docgen/ApiExporter.java
@@ -85,6 +85,7 @@
         param.setName(par.getName());
         param.setType(par.getType());
         param.setDoc(par.getDocumentation());
+        param.setDefaultValue(par.getDefaultValue());
         callable.addParam(param);
       }
       callable.setReturnType(meth.getReturnType());
diff --git a/src/main/java/com/google/devtools/build/docgen/skylark/SkylarkParamDoc.java b/src/main/java/com/google/devtools/build/docgen/skylark/SkylarkParamDoc.java
index 74d26a9..81f0e35 100644
--- a/src/main/java/com/google/devtools/build/docgen/skylark/SkylarkParamDoc.java
+++ b/src/main/java/com/google/devtools/build/docgen/skylark/SkylarkParamDoc.java
@@ -71,6 +71,10 @@
     return param.name();
   }
 
+  public String getDefaultValue() {
+    return param.defaultValue();
+  }
+
   @Override
   public String getDocumentation() {
     return SkylarkDocUtils.substituteVariables(param.doc());