message: Fix some more memory leaks in the Metal backend.
diff: @@ -43,6 +43,7 @@ namespace backend { namespace metal {
  ASSERT(compute == nil);
  if (blit != nil) {
  [blit endEncoding];
  + [blit release];
  blit = nil;
  }
  }
  @@ -64,6 +65,7 @@ namespace backend { namespace metal {
  void EndCompute() {
  ASSERT(compute != nil);
  [compute endEncoding];
  + [compute release];
  compute = nil;
  }
  @@ -71,6 +73,7 @@ namespace backend { namespace metal {
  ASSERT(currentRenderPass);
  if (render != nil) {
  [render endEncoding];
  + [render release];
  render = nil;
  }
  @@ -141,12 +144,14 @@ namespace backend { namespace metal {
  }
  render = [commandBuffer renderCommandEncoderWithDescriptor:descriptor];
  + [descriptor release];
  // TODO(cwallez@chromium.org): does any state need to be reset?
  }
  void EndSubpass() {
  ASSERT(render != nil);
  [render endEncoding];
  + [render release];
  render = nil;
  }
  };
  