Re-enable WebView tests

These WebView tests were incorrectly disabled.
See referenced bugs for further info.

BUG=419692,419690

Review URL: https://codereview.chromium.org/654533003

Cr-Commit-Position: refs/heads/master@{#299449}

tools/perf/benchmarks/blink_perf.py

@@ -124,7 +124,6 @@ class BlinkPerfCSS(benchmark.Benchmark):
     return _CreatePageSetFromPath(path, SKIPPED_FILE)
 
 
-@benchmark.Disabled('android-webview') # crbug.com/419692
 class BlinkPerfCanvas(benchmark.Benchmark):
   tag = 'canvas'
   test = _BlinkPerfMeasurement
@@ -206,7 +205,6 @@ class BlinkPerfShadowDOM(benchmark.Benchmark):
     return _CreatePageSetFromPath(path, SKIPPED_FILE)
 
 
-@benchmark.Disabled('android-webview') # crbug.com/419690
 class BlinkPerfXMLHttpRequest(benchmark.Benchmark):
   tag = 'xml_http_request'
   test = _BlinkPerfMeasurement