Update Gradle version from 4.1 to 4.4

In Gradle 4.4, it is a bug to resolve a configuration before the lint task is
created ([see [] Therefore, to upgrade
gradle version, we need to change the "generateJavadoc" task to remove using
files() call during initialization phase, but change move this to doFirst()
instead.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190634090

RELEASENOTES.md

@@ -2,6 +2,8 @@
 
 ### 2.7.2 ###
 
+* Gradle: Upgrade Gradle version from 4.1 to 4.4 so it can work with Android
+  Studio 3.1 ([#3708](https://github.com/google/ExoPlayer/issues/3708)).
 * Match codecs starting with "mp4a" to different Audio MimeTypes
   ([#3779](https://github.com/google/ExoPlayer/issues/3779)).
 * Fix ANR issue on Redmi 4X and Redmi Note 4
@@ -85,7 +87,7 @@
   ([#3630](https://github.com/google/ExoPlayer/issues/3630)).
 * DASH:
   * Support in-band Emsg events targeting the player with scheme id
-    `urn:mpeg:dash:event:2012` and scheme values "1", "2" and "3".
+    "urn:mpeg:dash:event:2012" and scheme values "1", "2" and "3".
   * Support EventStream elements in DASH manifests.
 * HLS:
     * Add opt-in support for chunkless preparation in HLS. This allows an

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip

javadoc_library.gradle

@@ -20,8 +20,6 @@ android.libraryVariants.all { variant ->
         description = "Generates Javadoc for the ${javadocTitle}."
         title = "ExoPlayer ${javadocTitle}"
         source = variant.javaCompile.source
-        classpath = files(variant.javaCompile.classpath.files,
-	                  project.android.getBootClasspath())
         options {
             links "http://docs.oracle.com/javase/7/docs/api/"
             linksOffline "https://developer.android.com/reference",
@@ -30,6 +28,12 @@ android.libraryVariants.all { variant ->
         }
         exclude "**/BuildConfig.java"
         exclude "**/R.java"
+        doFirst {
+            classpath =
+                files(
+                    variant.javaCompile.classpath.files,
+                    project.android.getBootClasspath())
+        }
         doLast {
             copy {
                 from "src/main/javadoc"