Revert "[coverage] Remove Clang coverage dump at fast exit."

This reverts commit 935afaa8.

Reason for revert: Per Wez's comments, this change doesn't do what we expect.

Original change's description:
> [coverage] Remove Clang coverage dump at fast exit.
> 
> The coverage dump in TerminateCurrentProcessImmediately is currently
> blocking us from gathering coverage for sandboxed processes, because
> it corrupts the data from those processes.
> 
> This is a temporary workaround, until we implement a proper solution
> for the data corruption.
> 
> Bug: 993537
> Change-Id: Idd4669f3d41b349247161e9611e52ca00a9e75ac
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752926
> Commit-Queue: Sajjad Mirza <sajjadm@chromium.org>
> Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#686667}

TBR=wez@chromium.org,nodir@chromium.org,liaoyuke@chromium.org,sajjadm@chromium.org

Change-Id: I454f38a7a708e6b7cff36f0603d03e96332d37ce
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 993537
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1753549Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686825}

base/process/process_posix.cc

@@ -10,6 +10,7 @@
 #include <sys/resource.h>
 #include <sys/wait.h>
 
+#include "base/clang_coverage_buildflags.h"
 #include "base/debug/activity_tracker.h"
 #include "base/files/scoped_file.h"
 #include "base/logging.h"
@@ -22,6 +23,9 @@
 #include <sys/event.h>
 #endif
 
+#if BUILDFLAG(CLANG_COVERAGE)
+#include "base/test/clang_coverage.h"
+#endif
 
 namespace {
 
@@ -272,6 +276,9 @@ bool Process::CanBackgroundProcesses() {
 
 // static
 void Process::TerminateCurrentProcessImmediately(int exit_code) {
+#if BUILDFLAG(CLANG_COVERAGE)
+  WriteClangCoverageProfile();
+#endif
   _exit(exit_code);
 }