Check EXT_color_buffer_float extension is available

If the extension isn't available, we cannot read from fbo attaching
float texture attachment. This CL adds error message when the extension
is not available.

BUG=369849, 624436

Review-Url: https://codereview.chromium.org/2565703002
Cr-Commit-Position: refs/heads/master@{#437744}

content/test/data/media/getusermedia-depth-capture.html

@@ -144,9 +144,9 @@
     canvas.width = 96;
     canvas.height = 96;
     var gl = canvas.getContext('webgl');
-    if(!gl)
+    if (!gl)
       return error({name:"WebGL is not available."});
-    if(!gl.getExtension("OES_texture_float"))
+    if (!gl.getExtension("OES_texture_float"))
       return error({name:"OES_texture_float extension is not available."});
     return testVideoToTexture(gl, video, gl.RGBA, gl.RGBA, gl.FLOAT,
                               readAndVerifyRGBA32F, success, error);
@@ -158,7 +158,7 @@
     canvas.width = 96;
     canvas.height = 96;
     var gl = canvas.getContext('webgl');
-    if(!gl)
+    if (!gl)
       return error({name:"WebGL is not available."});
     return testVideoToTexture(gl, video, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE,
                               readAndVerifyRGBA8, success, error);
@@ -170,9 +170,10 @@
     canvas.width = 96;
     canvas.height = 96;
     var gl = canvas.getContext('webgl2');
-    if(!gl)
+    if (!gl)
       return error({name:"WebGL2 is not available."});
-    var color_buffer_float_ext = gl.getExtension('EXT_color_buffer_float');
+    if (!gl.getExtension('EXT_color_buffer_float'))
+      return error({name:"EXT_color_buffer_float extension is not available."});
     return testVideoToTexture(gl, video, gl.R32F, gl.RED, gl.FLOAT,
                               readAndVerifyR32F, success, error);
   }