Update Memory.RendererUsed only after Blink is initialized

Yak shaving to land https://codereview.chromium.org/380533003/

Before the patch, |MemoryObserver| called |GetMemoryUsageKB()| without
any check, which is only valid after webkit is initialized.
GetMemoryUsageKB queries |v8::Isolate::GetCurrent()| internally, but the
query fails on DCHECK on debug builds.

This patch moves the |MemoryObserver| instantiation inside |RenderThreadImpl::EnsureWebKitInitialized|.

BUG=None

Review URL: https://codereview.chromium.org/380603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282321 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed