Fix for building with ancient toolchain

At Opera we test our SDK on an old MIPS device with a
peculiar toolchain. To be able to compile ImageDocument.o,
we need to call std::round(), not just round().

BUG=none

Review-Url: https://codereview.chromium.org/2548783002
Cr-Commit-Position: refs/heads/master@{#440950}

third_party/WebKit/Source/core/html/ImageDocument.cpp

@@ -403,7 +403,7 @@ void ImageDocument::updateImageStyle() {
           scale = viewportWidth / static_cast<double>(calculateDivWidth());
         }
 
-        newCheckerSize = round(std::max(1.0, newCheckerSize / scale));
+        newCheckerSize = std::round(std::max(1.0, newCheckerSize / scale));
       } else {
         // In desktop mode, the user can click on the image to zoom in or out.
         DCHECK_EQ(m_shrinkToFitMode, Desktop);