Add safety checks and reenable Canvas2D/WebGL trace_tests.

content/test/gpu/gpu_tests/trace_test.py

 # Copyright (c) 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 from gpu_tests import gpu_test_base
 from gpu_tests import trace_test_expectations
 import page_sets
 
 from telemetry.page import page_test
 from telemetry.timeline import model as model_module
 from telemetry.timeline import tracing_config
 
 TOPLEVEL_GL_CATEGORY = 'gpu_toplevel'
 TOPLEVEL_SERVICE_CATEGORY = 'disabled-by-default-gpu.service'
 TOPLEVEL_DEVICE_CATEGORY = 'disabled-by-default-gpu.device'
 TOPLEVEL_CATEGORIES = [TOPLEVEL_SERVICE_CATEGORY, TOPLEVEL_DEVICE_CATEGORY]
 
 test_harness_script = r"""
   var domAutomationController = {};
 
   domAutomationController._finished = false;
 
   domAutomationController.setAutomationId = function(id) {}
 
   domAutomationController.send = function(msg) {
     // Issue a read pixel to synchronize the gpu process to ensure
     // the asynchronous category enabling is finished.
-    var canvas = document.createElement("canvas")
-    canvas.width = 1;
-    canvas.height = 1;
-    var gl = canvas.getContext("webgl");
-    gl.clear(gl.COLOR_BUFFER_BIT);
-    var id = new Uint8Array(4);
-    gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, id);
+    var temp_canvas = document.createElement("canvas")
+    temp_canvas.width = 1;
+    temp_canvas.height = 1;
+    var temp_gl = temp_canvas.getContext("experimental-webgl") ||
+                  temp_canvas.getContext("webgl");
+    if (temp_gl) {
+      temp_gl.clear(temp_gl.COLOR_BUFFER_BIT);
+      var id = new Uint8Array(4);
+      temp_gl.readPixels(0, 0, 1, 1, temp_gl.RGBA, temp_gl.UNSIGNED_BYTE, id);
+    } else {
+      console.log('Failed to get WebGL context.');
+    }
 
     domAutomationController._finished = true;
   }
 
   window.domAutomationController = domAutomationController;
 """
 
 
 class TraceValidatorBase(gpu_test_base.ValidatorBase):
   def GetCategoryName(self):
@@ skipping 68 matching lines @@
   """Tests GPU Device traces show up on devices that support it."""
   test = _DeviceTraceValidator
   name = 'DeviceTraceTest'
 
   @classmethod
   def Name(cls):
     return 'device_trace_test'
 
   def _CreateExpectations(self):
     return trace_test_expectations.DeviceTraceTestExpectations()