[piexwasm] Accept RAW image source data in a File

piex-wasm assumes a fileSystemURL input as the RAW image source. Allow
other users to input the RAW image source in a File.

Add readFile helper, and make fileSystemURL and File source inputs use
it to read the file.

fileSystemURL case has automated test coverage, so readFIle is tested,
so no change in files app behavior.

Bug: 1132695
Change-Id: Ic05c5b5a2178826445221448824f8ef41dc81ea7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437084Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Auto-Submit: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811898}

ui/file_manager/image_loader/piex_loader.js

@@ -114,10 +114,9 @@ function PiexLoaderResponse(data) {
  * Returns the source data.
  *
  * If the source is an ArrayBuffer, return it. Otherwise assume the source is
- * is DOM file system URL: resolve the associated file system entry, and read
- * and return its content in an ArrayBuffer.
+ * is a File or DOM fileSystemURL and return its content in an ArrayBuffer.
  *
- * @param {string|!ArrayBuffer} source
+ * @param {!ArrayBuffer|!File|string} source
  * @return {!Promise<!ArrayBuffer>}
  */
 function readSourceData(source) {
@@ -130,11 +129,11 @@ function readSourceData(source) {
      * Reject the Promise on fileEntry URL resolve or file read failures.
      */
     function failure(error) {
-      reject(new Error('Reading file system: ' + error));
+      reject(new Error('Reading file system: ' + (error.message || error)));
     }
 
     /**
-     * Returns true if the fileEntry file size is within sensible limits.
+     * Returns true if the file size is within sensible limits.
      * @param {number} size - file size.
      * @return {boolean}
      */
@@ -143,25 +142,39 @@ function readSourceData(source) {
     }
 
     /**
-     * Reads the fileEntry's content into an ArrayBuffer: resolve Promise
-     * with the ArrayBuffer result or reject the Promise on failure.
-     * @param {!Entry} entry - file system entry of |url|.
+     * Reads the file content to an ArrayBuffer. Resolve the Promise with
+     * the ArrayBuffer result, or reject the Promise on failure.
+     * @param {!File} file - file to read.
+     */
+    function readFile(file) {
+      if (valid(file.size)) {
+        const reader = new FileReader();
+        reader.onerror = failure;
+        reader.onload = (_) => resolve(reader.result);
+        reader.readAsArrayBuffer(file);
+      } else {
+        failure('invalid file size: ' + file.size);
+      }
+    }
+
+    /**
+     * Resolve the fileEntry's file then read it with readFile, or reject
+     * the Promise on failure.
+     * @param {!Entry} entry - file system entry.
      */
     function readEntry(entry) {
       const fileEntry = /** @type {!FileEntry} */ (entry);
       fileEntry.file((file) => {
-        if (valid(file.size)) {
-          const reader = new FileReader();
-          reader.onerror = failure;
-          reader.onload = (_) => resolve(reader.result);
-          reader.readAsArrayBuffer(file);
-        } else {
-          failure('invalid file size: ' + file.size);
-        }
+        readFile(file);
       }, failure);
     }
 
-    const url = /** @type {string} */ (source);
+    if (source instanceof File) {
+      readFile(/** @type {!File} */ (source));
+      return;
+    }
+
+    const url = /** @type {string} fileSystemURL */ (source);
     globalThis.webkitResolveLocalFileSystemURL(url, readEntry, failure);
   });
 }
@@ -481,7 +494,7 @@ function PiexLoader() {}
  * to reload the page. Callback |onPiexModuleFailed| is used to indicate that
  * the caller should initiate failure recovery steps.
  *
- * @param {string|!ArrayBuffer} source
+ * @param {!ArrayBuffer|!File|string} source
  * @param {!function()} onPiexModuleFailed
  * @return {!Promise<!PiexLoaderResponse>}
  */