[WebProfilerBundle] Fixed profiler toolbar icons for XHTML.
bug #9948 [WebProfilerBundle] Fixed profiler toolbar icons for XHTML. (rafalwrzeszcz)

This PR was squashed before being merged into the 2.3 branch (closes #9948).

Discussion
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[WebProfilerBundle] Fixed profiler toolbar icons for XHTML.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | n/a
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Profiler page itself is entirely autonomic, but toolbar is not - unfortunately currently it doesn't work in XHTML documents :(.

#9877 backported to `2.3` branch.

Commits
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296c4d1 [WebProfilerBundle] Fixed profiler toolbar icons for XHTML.