CronetDataSource: Fix thread safety issue with requestProperties

The access in fillCurrentRequestPostBody wasn't protected with
synchronization. Furthermore, just synchronizing it wouldn't be
sufficient, since what we really need to check is whether the
Content-Type header has been added to the UrlRequest.Builder.
The contents of requestProperties may have changed between the
headers being added to UrlRequest.Builder and the call to
fillCurrentRequestPostBody.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135376904

extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/CronetDataSource.java

@@ -212,13 +212,8 @@ public class CronetDataSource extends UrlRequest.Callback implements HttpDataSou
 
     operation.close();
     resetConnectTimeout();
-
     currentDataSpec = dataSpec;
-    UrlRequest.Builder urlRequestBuilder = new UrlRequest.Builder(dataSpec.uri.toString(), this,
-        executor, cronetEngine);
-    fillCurrentRequestHeader(urlRequestBuilder);
-    fillCurrentRequestPostBody(urlRequestBuilder, dataSpec);
-    currentUrlRequest = urlRequestBuilder.build();
+    currentUrlRequest = buildRequest(dataSpec);
     currentUrlRequest.start();
     boolean requestStarted = blockUntilConnectTimeout();
 
@@ -423,36 +418,35 @@ public class CronetDataSource extends UrlRequest.Callback implements HttpDataSou
 
   // Internal methods.
 
-  private void fillCurrentRequestHeader(UrlRequest.Builder urlRequestBuilder) {
+  private UrlRequest buildRequest(DataSpec dataSpec) throws OpenException {
+    UrlRequest.Builder requestBuilder = new UrlRequest.Builder(dataSpec.uri.toString(), this,
+        executor, cronetEngine);
+    // Set the headers.
     synchronized (requestProperties) {
+      if (dataSpec.postBody != null && !requestProperties.containsKey(CONTENT_TYPE)) {
+        throw new OpenException("POST request must set Content-Type", dataSpec, Status.IDLE);
+      }
       for (Entry<String, String> headerEntry : requestProperties.entrySet()) {
-        urlRequestBuilder.addHeader(headerEntry.getKey(), headerEntry.getValue());
+        requestBuilder.addHeader(headerEntry.getKey(), headerEntry.getValue());
       }
     }
-    if (currentDataSpec.position == 0 && currentDataSpec.length == C.LENGTH_UNSET) {
-      // Not required.
-      return;
-    }
-    StringBuilder rangeValue = new StringBuilder();
-    rangeValue.append("bytes=");
-    rangeValue.append(currentDataSpec.position);
-    rangeValue.append("-");
-    if (currentDataSpec.length != C.LENGTH_UNSET) {
-      rangeValue.append(currentDataSpec.position + currentDataSpec.length - 1);
-    }
-    urlRequestBuilder.addHeader("Range", rangeValue.toString());
-  }
-
-  private void fillCurrentRequestPostBody(UrlRequest.Builder urlRequestBuilder, DataSpec dataSpec)
-      throws HttpDataSourceException {
-    if (dataSpec.postBody == null) {
-      return;
+    // Set the Range header.
+    if (currentDataSpec.position != 0 || currentDataSpec.length != C.LENGTH_UNSET) {
+      StringBuilder rangeValue = new StringBuilder();
+      rangeValue.append("bytes=");
+      rangeValue.append(currentDataSpec.position);
+      rangeValue.append("-");
+      if (currentDataSpec.length != C.LENGTH_UNSET) {
+        rangeValue.append(currentDataSpec.position + currentDataSpec.length - 1);
+      }
+      requestBuilder.addHeader("Range", rangeValue.toString());
     }
-    if (!requestProperties.containsKey(CONTENT_TYPE)) {
-      throw new OpenException("POST request must set Content-Type", dataSpec, Status.IDLE);
+    // Set the body.
+    if (dataSpec.postBody != null) {
+      requestBuilder.setUploadDataProvider(new ByteArrayUploadDataProvider(dataSpec.postBody),
+          executor);
     }
-    urlRequestBuilder.setUploadDataProvider(new ByteArrayUploadDataProvider(dataSpec.postBody),
-        executor);
+    return requestBuilder.build();
   }
 
   private boolean blockUntilConnectTimeout() {