Support lossy and lossless <canvas>.toDataURL for webp

Source/platform/graphics/ImageBuffer.cpp

Index: Source/platform/graphics/ImageBuffer.cpp
diff --git a/Source/platform/graphics/ImageBuffer.cpp b/Source/platform/graphics/ImageBuffer.cpp
index ece9dc7433d21ba3177ece5950bb03cc5136dd95..809f556cda7292a611a66a97af1ca3871aa2c925 100644
--- a/Source/platform/graphics/ImageBuffer.cpp
+++ b/Source/platform/graphics/ImageBuffer.cpp
@@ -351,6 +351,12 @@ static bool encodeImage(const ImageDataBuffer& source, const String& mimeType, c
             compressionQuality = static_cast<int>(*quality * 100 + 0.5);
         if (!JPEGImageEncoder::encode(source, compressionQuality, encodedImage))
             return false;
+    } else if (mimeType == "image/webplossless") {
+        int compressionQuality = WEBPImageEncoder::DefaultCompressionQuality;
+        if (quality && *quality >= 0.0 && *quality <= 1.0)
+            compressionQuality = static_cast<int>(*quality * 100 + 0.5);
+        if (!WEBPImageEncoder::encode(source, compressionQuality, encodedImage, WEBPImageEncoder::Lossless))
+            return false;
     } else if (mimeType == "image/webp") {
         int compressionQuality = WEBPImageEncoder::DefaultCompressionQuality;
         if (quality && *quality >= 0.0 && *quality <= 1.0)
@@ -374,7 +380,13 @@ String ImageDataBuffer::toDataURL(const String& mimeType, const double* quality)
     if (!encodeImage(*this, mimeType, quality, &encodedImage))
         return "data:,";
 
-    return "data:" + mimeType + ";base64," + base64Encode(encodedImage);
+    // webplossless is an encoder selector: map it to the actual mimeType "image/webp".
+

[acterhd, 2015/08/27 17:18:19]

I'm used ternary operator for replace mimes. 

+    String encodedImageMimeType = mimeType;
+    if (mimeType == "image/webplossless")
+        encodedImageMimeType = String("image/webp");
+
+    return "data:" + encodedImageMimeType + ";base64," + base64Encode(encodedImage);
 }
 
 } // namespace blink