Revert "Reland "metrics: Initialize persistent metric allocator early.""

This reverts commit 63fab7f6.

Reason for revert: breaking android-go-perf on chrome perf waterfall
BUG:875640

Original change's description:
> Reland "metrics: Initialize persistent metric allocator early."
> 
> This is a reland of 0cdc1458
> 
> Original change's description:
> > metrics: Initialize persistent metric allocator early.
> >
> > The PersistentMemoryAllocator in the gpu (and other) process is created
> > asynchronously. If any uma-histogram is reported before that time, then
> > those Histograms are not stored in the shared memory. This has some
> > implications:
> >  . If the process crashes (which is common for the gpu process on
> >    android), then these metrics are lost.
> >  . If the process stays alive, then the metrics are reported
> >    periodically, but because it is buffered, it doesn't match up
> >    correctly with the other metrics that are reported in the shared
> >    memory.
> >
> > The allocator is created in response to a message from the browser,
> > which includes the handle for the shared memory to use for the allocator.
> > The browser waits until the process has been launched and connected.
> > So this happens much later, compared to other messages which are sent
> > from browser over mojo without waiting for the connection to have
> > been established first. Therefore, change this so that the browser
> > immediately shares the shared-memory segment with the gpu process. mojo
> > takes care of waiting for the process-launch etc.
> >
> > BUG=865179, 778749
> >
> > Change-Id: Iccd3d4422de3e22ead4bc6510afc5ea207bf6b6e
> > Reviewed-on: https://chromium-review.googlesource.com/1174709
> > Reviewed-by: Brian White <bcwhite@chromium.org>
> > Reviewed-by: Avi Drissman <avi@chromium.org>
> > Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#583673}
> TBR=avi,sadrul
> 
> Bug: 865179, 778749
> Change-Id: I205221ed82b073464e1c4d52593ba727ebc211a5
> Reviewed-on: https://chromium-review.googlesource.com/1179346
> Reviewed-by: Matthew Jones <mdjones@chromium.org>
> Commit-Queue: Matthew Jones <mdjones@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#584203}

TBR=avi@chromium.org,sadrul@chromium.org,bcwhite@chromium.org,mdjones@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 865179, 778749
Change-Id: I7fd057c81494dff8072a2e847510821ec6ff8530
Reviewed-on: https://chromium-review.googlesource.com/1180741Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#584342}

content/browser/browser_child_process_host_impl.cc

@@ -178,7 +178,6 @@ BrowserChildProcessHostImpl::BrowserChildProcessHostImpl(
 
   // Create a persistent memory segment for subprocess histograms.
   CreateMetricsAllocator();
-  ShareMetricsAllocatorToProcess();
 }
 
 BrowserChildProcessHostImpl::~BrowserChildProcessHostImpl() {
@@ -390,6 +389,7 @@ void BrowserChildProcessHostImpl::OnChannelConnected(int32_t peer_pid) {
   delegate_->OnChannelConnected(peer_pid);
 
   if (IsProcessLaunched()) {
+    ShareMetricsAllocatorToProcess();
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::BindOnce(&NotifyProcessLaunchedAndConnected, data_.Duplicate()));
@@ -608,6 +608,7 @@ void BrowserChildProcessHostImpl::OnProcessLaunched() {
   delegate_->OnProcessLaunched();
 
   if (is_channel_connected_) {
+    ShareMetricsAllocatorToProcess();
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::BindOnce(&NotifyProcessLaunchedAndConnected, data_.Duplicate()));