Improve Javadoc postprocessing

- Remove stray extra "/" from postprocessed oracle URLs
- Remove date lines so the Javadoc diff better shows what
  actually changed between releases

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190973079

javadoc_combined.gradle

@@ -49,7 +49,7 @@ class CombinedJavadocPlugin implements Plugin<Project> {
             }
           }
           doLast {
-            project.javadocFixLinks()
+            project.fixJavadoc()
           }
         }
       }

javadoc_library.gradle

@@ -37,7 +37,7 @@ android.libraryVariants.all { variant ->
                     project.android.getBootClasspath())
         }
         doLast {
-            project.javadocFixLinks()
+            project.fixJavadoc()
         }
     }
 }

javadoc_util.gradle

@@ -11,21 +11,29 @@
 // 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.
-ext.javadocFixLinks = {
+ext.fixJavadoc = {
+  def javadocPath = "${project.buildDir}/docs/javadoc"
   // Fix external Android links to target the top frame.
   def androidRoot = "https://developer.android.com/reference/"
   def androidLink = "<a href=\"(${androidRoot}.*?)\\?is-external=true\""
   def androidFixed = "<a href=\"\\1\" target=\"_top\""
-  ant.replaceregexp(
-      match:androidLink, replace:androidFixed, flags:'g', byline:true) {
-    fileset(dir: "${project.buildDir}/docs/javadoc")
+  ant.replaceregexp(match:androidLink, replace:androidFixed, flags:'g') {
+    fileset(dir: "${javadocPath}", includes: "**/*.html")
   }
   // Fix external Oracle links to use frames and target the top frame.
   def oracleRoot = "https://docs.oracle.com/javase/7/docs/api/"
   def oracleLink = "<a href=\"(${oracleRoot})(.*?)\\?is-external=true\""
-  def oracleFixed = "<a href=\"\\1/index.html\\?\\2\" target=\"_top\""
-  ant.replaceregexp(
-      match:oracleLink, replace:oracleFixed, flags:'g', byline:true) {
-    fileset(dir: "${project.buildDir}/docs/javadoc")
+  def oracleFixed = "<a href=\"\\1index.html\\?\\2\" target=\"_top\""
+  ant.replaceregexp(atch:oracleLink, replace:oracleFixed, flags:'g') {
+    fileset(dir: "${javadocPath}", includes: "**/*.html")
+  }
+  // Remove date metadata that changes every time Javadoc is generated.
+  def javadocGeneratedBy = "<!-- Generated by javadoc.*?-->\n"
+  ant.replaceregexp(match:javadocGeneratedBy, replace:"") {
+    fileset(dir: "${javadocPath}", includes: "**/*.html")
+  }
+  def dateMeta = "<meta name=\"date\".*?>\n"
+  ant.replaceregexp(match:dateMeta, replace:"") {
+    fileset(dir: "${javadocPath}", includes: "**/*.html")
   }
 }