gpu: Enable WebGL on Mali-400 GPUs that support EXT_robustness

Enable WebGL on Mali-400 GPUs that support the EXT_robustness extension
but do *not* send context reset notifications. The reason we can do
this is that virtualized contexts are not used on these devices, so
badly behaving WebGL shaders do not affect other GL contexts. This means
that the user can close or reload the WebGL tab and other tabs in the
browser remain responsive.

BUG=288731,416690
TEST=https://www.khronos.org/registry/webgl/conformance-suites/1.0.1/extra/slow-shader-example.html on a Galaxy Tab 3

Review URL: https://codereview.chromium.org/24037006

Cr-Commit-Position: refs/heads/master@{#296768}

gpu/config/software_rendering_list_json.cc

@@ -18,7 +18,7 @@ const char kSoftwareRenderingListJson[] = LONG_STRING_CONST(
 {
   "name": "software rendering list",
   // Please update the version number whenever you change this file.
-  "version": "9.7",
+  "version": "9.8",
   "entries": [
     {
       "id": 1,
@@ -795,6 +795,10 @@ LONG_STRING_CONST(
             "op": "=",
             "value": "33362"
           }
+        },
+        {
+          "gl_renderer": "Mali-400.*",
+          "gl_extensions": ".*EXT_robustness.*"
         }
       ],
       "features": [