canvas.getContext with alpha:undefined should behave like alpha:true

LayoutTests/fast/canvas/webgl/context-attributes-alpha-depth-stencil-antialias.html

Index: LayoutTests/fast/canvas/webgl/context-attributes-alpha-depth-stencil-antialias.html
diff --git a/LayoutTests/fast/canvas/webgl/context-attributes-alpha-depth-stencil-antialias.html b/LayoutTests/fast/canvas/webgl/context-attributes-alpha-depth-stencil-antialias.html
index 1d97dfafffea6b47508cfeaad2040abd2bec4e4a..538f0defa531d4fff360cc197ca7b1e826d72b28 100644
--- a/LayoutTests/fast/canvas/webgl/context-attributes-alpha-depth-stencil-antialias.html
+++ b/LayoutTests/fast/canvas/webgl/context-attributes-alpha-depth-stencil-antialias.html
@@ -143,12 +143,13 @@ function testDefault()
 function testAlpha(alpha)
 {
     debug("Testing alpha = " + alpha);
-    if (alpha) {
-        shouldBeNonNull("gl = getWebGL(1, 1, { alpha: true, depth: false, stencil: false, antialias: false }, [ 0, 0, 0, 0 ], 1, 0)");
-        shouldBeTrue("gl.getParameter(gl.ALPHA_BITS) >= 8");
-    } else {
+    if (alpha == false) {
         shouldBeNonNull("gl = getWebGL(1, 1, { alpha: false, depth: false, stencil: false, antialias: false }, [ 0, 0, 0, 0 ], 1, 0)");
         shouldBeTrue("gl.getParameter(gl.ALPHA_BITS) == 0");
+    } else {
+        window.alpha = alpha;
+        shouldBeNonNull("gl = getWebGL(1, 1, { alpha: alpha, depth: false, stencil: false, antialias: false }, [ 0, 0, 0, 0 ], 1, 0)");
+        shouldBeTrue("gl.getParameter(gl.ALPHA_BITS) >= 8");
     }
     shouldBeTrue("gl.getParameter(gl.RED_BITS) >= 8");
     shouldBeTrue("gl.getParameter(gl.GREEN_BITS) >= 8");
@@ -157,7 +158,7 @@ function testAlpha(alpha)
     shouldBeTrue("gl.getParameter(gl.STENCIL_BITS) == 0");
 
     shouldBeNonNull("contextAttribs = gl.getContextAttributes()");
-    shouldBeTrue("contextAttribs.alpha == " + alpha);
+    shouldBeTrue("contextAttribs.alpha == " + (alpha || alpha == undefined || alpha == null ? true : false));
 
     var buf = new Uint8Array(1 * 1 * 4);
     gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, buf);
@@ -338,6 +339,8 @@ function runTest()
     testDefault();
     testAlpha(true);
     testAlpha(false);
+    testAlpha(undefined);
+    testAlpha(null);
     testDepth(true);
     testDepth(false);
     testStencilAndDepth(true, false);