Fix blink_perf.canvas failure on chromium.perf

PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html

Index: PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
diff --git a/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html b/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
index 1118122892b5eb3d2560abac1e5709130d1f01b9..07c74ef67f122457223f5e141092780cc1ba14bf 100644
--- a/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
+++ b/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
@@ -7,7 +7,7 @@
 var canvas2D = document.createElement("canvas");
 var ctx2D = canvas2D.getContext("2d");
 var canvas3D = document.createElement('canvas');
-var gl = canvas3D.getContext('experimental-webgl');
+var gl = canvas3D.getContext('webgl');
 if (!gl)
     CanvasRunner.logFatalError("\nWebGL is not supported or enabled on this platform!\n");