Move the colour conversion to jpg.js

Benchmarking shows that this improves performance for the invitation document
from https://github.com/mozilla/pdf.js/issues/3809 by 35%

src/core/image.js

@@ -502,7 +502,7 @@ var PDFImage = (function PDFImageClosure() {
 
       // Rows start at byte boundary.
       var rowBytes = (originalWidth * numComps * bpc + 7) >> 3;
-      var imgArray = this.getImageBytes(originalHeight * rowBytes);
+      var imgArray;
 
       if (!forceRGBA) {
         // If it is a 1-bit-per-pixel grayscale (i.e. black-and-white) image
@@ -522,6 +522,7 @@ var PDFImage = (function PDFImageClosure() {
             drawWidth === originalWidth && drawHeight === originalHeight) {
           imgData.kind = kind;
 
+          imgArray = this.getImageBytes(originalHeight * rowBytes);
           // If imgArray came from a DecodeStream, we're safe to transfer it
           // (and thus neuter it) because it will constitute the entire
           // DecodeStream's data.  But if it came from a Stream, we need to
@@ -537,6 +538,14 @@ var PDFImage = (function PDFImageClosure() {
           return imgData;
         }
       }
+      if (this.image instanceof JpegStream) {
+        imgData.kind = ImageKind.RGB_24BPP;
+        imgData.data = this.getImageBytes(originalHeight * rowBytes,
+                                          drawWidth, drawHeight);
+        return imgData;
+      }
+
+      imgArray = this.getImageBytes(originalHeight * rowBytes);
       // imgArray can be incomplete (e.g. after CCITT fax encoding).
       var actualHeight = 0 | (imgArray.length / rowBytes *
                          drawHeight / originalHeight);
@@ -597,7 +606,7 @@ var PDFImage = (function PDFImageClosure() {
         length = width * height;
         if (this.needsDecode) {
           // invert and scale to {0, 255}
-          for (var i = 0; i < length; ++i) {
+          for (i = 0; i < length; ++i) {
             buffer[i] = (comps[i] - 1) & 255;
           }
         } else {
@@ -620,8 +629,11 @@ var PDFImage = (function PDFImageClosure() {
       }
     },
 
-    getImageBytes: function PDFImage_getImageBytes(length) {
+    getImageBytes: function PDFImage_getImageBytes(length,
+                                                   drawWidth, drawHeight) {
       this.image.reset();
+      this.image.drawWidth = drawWidth;
+      this.image.drawHeight = drawHeight;
       return this.image.getBytes(length);
     }
   };

src/core/stream.js

@@ -873,9 +873,8 @@ var JpegStream = (function JpegStreamClosure() {
         jpegImage.colorTransform = this.colorTransform;
       }
       jpegImage.parse(this.bytes);
-      var width = jpegImage.width;
-      var height = jpegImage.height;
-      var data = jpegImage.getData(width, height);
+      var data = jpegImage.getData(this.drawWidth, this.drawHeight,
+                                   /* forceRGBoutput = */true);
       this.buffer = data;
       this.bufferLength = data.length;
       this.eof = true;
@@ -883,6 +882,12 @@ var JpegStream = (function JpegStreamClosure() {
       error('JPEG error: ' + e);
     }
   };
+
+  JpegStream.prototype.getBytes = function JpegStream_getBytes(length) {
+    this.ensureBuffer();
+    return this.buffer;
+  };
+
   JpegStream.prototype.getIR = function JpegStream_getIR() {
     return PDFJS.createObjectURL(this.bytes, 'image/jpeg');
   };

src/worker_loader.js

@@ -49,11 +49,11 @@ var otherFiles = [
   'core/stream.js',
   'core/worker.js',
   'core/arithmetic_decoder.js',
+  'core/jpg.js',
   'core/jpx.js',
   'core/jbig2.js',
   'core/bidi.js',
-  'core/murmurhash3.js',
-  '../external/jpgjs/jpg.js'
+  'core/murmurhash3.js'
 ];
 
 function loadInOrder(index, path, files) {