webgl: LowLatency and toDataURL work nicely together

There is a lot of flipping going on when using the
GL_MESA_framebuffer_flip_y extension.  toDataURL and
LowLatency have competing requirments when calling
CopyToPlatformTexture.

https://codepen.io/miguelao/full/WKZaqd
https://www.khronos.org/registry/webgl/sdk/tests/conformance/canvas/to-data-url-test.html

BUG=883362

Change-Id: Iafe11c23591a79f696b652a57f2d083258d3aa9c
Reviewed-on: https://chromium-review.googlesource.com/1237248Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593223}

third_party/blink/renderer/modules/webgl/webgl_rendering_context_base.cc

@@ -1602,8 +1602,9 @@ bool WebGLRenderingContextBase::CopyRenderingResultsFromDrawingBuffer(
     // CopyToPlatformTexture is done correctly. See crbug.com/794706.
     gl->Flush();
 
+    bool flip_y = is_origin_top_left_ && !canvas()->LowLatencyEnabled();
     return drawing_buffer_->CopyToPlatformTexture(
-        gl, GL_TEXTURE_2D, texture_id, true, is_origin_top_left_,
+        gl, GL_TEXTURE_2D, texture_id, true, flip_y,
         IntPoint(0, 0), IntRect(IntPoint(0, 0), drawing_buffer_->Size()),
         source_buffer);
   }
@@ -5198,7 +5199,7 @@ void WebGLRenderingContextBase::TexImageViaGPU(
           IntPoint(xoffset, yoffset), source_sub_rectangle);
     } else {
       WebGLRenderingContextBase* gl = source_canvas_webgl_context;
-      if (gl->is_origin_top_left_)
+      if (gl->is_origin_top_left_ && !canvas()->LowLatencyEnabled())
         flip_y = !flip_y;
       ScopedTexture2DRestorer restorer(gl);
       if (!gl->GetDrawingBuffer()->CopyToPlatformTexture(