fix(net): Fix HEAD requests in new Chromium (shaka-project#5180)

This makes it so that we no longer try to download the body of a head
response, in the http fetch plugin. This is necessary due to an upcoming
change to Chromium, where the body object of such responses is null.

Fixes shaka-project#5164

lib/net/http_fetch_plugin.js

@@ -120,65 +120,77 @@ shaka.net.HttpFetchPlugin = class {
       // not the body yet.
       headersReceived(shaka.net.HttpFetchPlugin.headersToGenericObject_(
           response.headers));
-      // Getting the reader in this way allows us to observe the process of
-      // downloading the body, instead of just waiting for an opaque promise to
-      // resolve.
-      // We first clone the response because calling getReader locks the body
-      // stream; if we didn't clone it here, we would be unable to get the
-      // response's arrayBuffer later.
-      const reader = response.clone().body.getReader();
-
-      const contentLengthRaw = response.headers.get('Content-Length');
-      const contentLength =
-          contentLengthRaw ? parseInt(contentLengthRaw, 10) : 0;
-
-      const start = (controller) => {
-        const push = async () => {
-          let readObj;
-          try {
-            readObj = await reader.read();
-          } catch (e) {
-            // If we abort the request, we'll get an error here.  Just ignore it
-            // since real errors will be reported when we read the buffer below.
-            shaka.log.v1('error reading from stream', e.message);
-            return;
-          }
-
-          if (!readObj.done) {
-            loaded += readObj.value.byteLength;
-            if (streamDataCallback) {
-              await streamDataCallback(readObj.value);
+
+      // In new versions of Chromium, HEAD requests now have a response body
+      // that is null.
+      // So just don't try to download the body at all, if it's a HEAD request,
+      // to avoid null reference errors.
+      // See: https://crbug.com/1297060
+      if (init.method != 'HEAD') {
+        goog.asserts.assert(response.body,
+            'non-HEAD responses should have a body');
+
+        // Getting the reader in this way allows us to observe the process of
+        // downloading the body, instead of just waiting for an opaque promise
+        // to resolve.
+        // We first clone the response because calling getReader locks the body
+        // stream; if we didn't clone it here, we would be unable to get the
+        // response's arrayBuffer later.
+        const reader = response.clone().body.getReader();
+
+        const contentLengthRaw = response.headers.get('Content-Length');
+        const contentLength =
+            contentLengthRaw ? parseInt(contentLengthRaw, 10) : 0;
+
+        const start = (controller) => {
+          const push = async () => {
+            let readObj;
+            try {
+              readObj = await reader.read();
+            } catch (e) {
+              // If we abort the request, we'll get an error here.  Just ignore
+              // it since real errors will be reported when we read the buffer
+              // below.
+              shaka.log.v1('error reading from stream', e.message);
+              return;
+            }
+
+            if (!readObj.done) {
+              loaded += readObj.value.byteLength;
+              if (streamDataCallback) {
+                await streamDataCallback(readObj.value);
+              }
+            }
+
+            const currentTime = Date.now();
+            // If the time between last time and this time we got progress event
+            // is long enough, or if a whole segment is downloaded, call
+            // progressUpdated().
+            if (currentTime - lastTime > 100 || readObj.done) {
+              progressUpdated(currentTime - lastTime, loaded - lastLoaded,
+                  contentLength - loaded);
+              lastLoaded = loaded;
+              lastTime = currentTime;
+            }
+
+            if (readObj.done) {
+              goog.asserts.assert(!readObj.value,
+                  'readObj should be unset when "done" is true.');
+              controller.close();
+            } else {
+              controller.enqueue(readObj.value);
+              push();
             }
-          }
-
-          const currentTime = Date.now();
-          // If the time between last time and this time we got progress event
-          // is long enough, or if a whole segment is downloaded, call
-          // progressUpdated().
-          if (currentTime - lastTime > 100 || readObj.done) {
-            progressUpdated(currentTime - lastTime, loaded - lastLoaded,
-                contentLength - loaded);
-            lastLoaded = loaded;
-            lastTime = currentTime;
-          }
-
-          if (readObj.done) {
-            goog.asserts.assert(!readObj.value,
-                'readObj should be unset when "done" is true.');
-            controller.close();
-          } else {
-            controller.enqueue(readObj.value);
-            push();
-          }
+          };
+          push();
         };
-        push();
-      };
-      // Create a ReadableStream to use the reader. We don't need to use the
-      // actual stream for anything, though, as we are using the response's
-      // arrayBuffer method to get the body, so we don't store the
-      // ReadableStream.
-      new ReadableStream({start}); // eslint-disable-line no-new
-      arrayBuffer = await response.arrayBuffer();
+        // Create a ReadableStream to use the reader. We don't need to use the
+        // actual stream for anything, though, as we are using the response's
+        // arrayBuffer method to get the body, so we don't store the
+        // ReadableStream.
+        new ReadableStream({start}); // eslint-disable-line no-new
+        arrayBuffer = await response.arrayBuffer();
+      }
     } catch (error) {
       if (abortStatus.canceled) {
         throw new shaka.util.Error(