Avoid pure virtual crash destroying RenderProcessUserData

When RenderProcessUserData is destroyed from the destructor of
RenderProcessHostImpl, it is done in the destructor of RenderProcessHost.
At this point RemoveObserver override is already freed, so RenderProcessHost
is pure virtual. This crash happens at least building with GCC:

    at /usr/include/c++/8/ext/new_allocator.h:140
    (this=0x7fffffffcb50, __in_chrg=<optimized out>) at /usr/include/c++/8/bits/stl_tree.h:964

We need to destroy RenderProcessUserData before that happens. To do that
we can just override RenderProcessHostDestroyed.

Bug: 910288
Change-Id: I38107b178829b0cb7494f5333b765e5b087d82cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645366
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666279}

chrome/browser/performance_manager/render_process_user_data.cc

@@ -116,4 +116,9 @@ void RenderProcessUserData::RenderProcessExited(
                      base::Unretained(process_node_.get()), info.exit_code));
 }
 
+void RenderProcessUserData::RenderProcessHostDestroyed(
+    content::RenderProcessHost* host) {
+  host->RemoveUserData(kRenderProcessUserDataKey);
+}
+
 }  // namespace performance_manager

chrome/browser/performance_manager/render_process_user_data.h

@@ -47,6 +47,7 @@ class RenderProcessUserData : public base::SupportsUserData::Data,
   void RenderProcessExited(
       content::RenderProcessHost* host,
       const content::ChildProcessTerminationInfo& info) override;
+  void RenderProcessHostDestroyed(content::RenderProcessHost* host) override;
 
   // All instances are linked together in a doubly linked list to allow orderly
   // destruction at browser shutdown time.