Suspend shared timers while blockingly closing databases

BUG=388771
R=michaeln@chromium.org

Review URL: https://codereview.chromium.org/409863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284785 0039d316-1c4b-4281-b951-d872f2087c98
RenderThreadImpl::HistogramCustomizer::HistogramCustomizer() {
  custom_histograms_.insert("V8.MemoryExternalFragmentationTotal");
  custom_histograms_.insert("V8.MemoryHeapSampleTotalCommitted");
  custom_histograms_.insert("V8.MemoryHeapSampleTotalUsed");
}

RenderThreadImpl::HistogramCustomizer::HistogramCustomizer() {
  custom_histograms_.insert("V8.MemoryExternalFragmentationTotal");
  custom_histograms_.insert("V8.MemoryHeapSampleTotalCommitted");
  custom_histograms_.insert("V8.MemoryHeapSampleTotalUsed");
}
