Revert "Reland: PR_SET_DUMPABLE 1 briefly if opening pagemap fails"

This reverts commit f889004d.

Reason for revert: http://crbug.com/1130358#c13

Original change's description:
> Reland: PR_SET_DUMPABLE 1 briefly if opening pagemap fails
> 
> This is often necessary on Android to read /proc/self/pagemap. Without
> prctl(PR_SET_DUMPABLE) opening this file fails in 94% of cases on
> Canary. This potentially leads to bias in reporting
> MappedAndResidentMemoryFootprint2.
> 
> What happened since it last landed as http://crrev.com/808298:
> * Setting the process back to non-dumpable was often returning an error
>   and hitting a (P)CHECK
> * In crash dumps logcat started right at the failure, so it is not
>   possible to see whether prctl(PR_SET_DUMPABLE, 1) succeeded prior to
>   the failure, my guess is that it failed too
> * In the reland, avoid prctl(SET_DUMPABLE, 0) if prctl(SET_DUMPABLE, 1)
>   failed before that
> 
> Bug: 1070618
> Change-Id: Ic9bfbdad6c72a1388eb80c3b6c9e6c772c8e431c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2421730
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: ssid <ssid@chromium.org>
> Commit-Queue: Egor Pasko <pasko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#809373}

TBR=pasko@chromium.org,ssid@chromium.org,rsesek@chromium.org

Change-Id: I3ae4695cca87eb4e878a195f84352fd5f19889d6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1070618
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425053Reviewed-by: Egor Pasko <pasko@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809744}

services/resource_coordinator/public/cpp/memory_instrumentation/os_metrics_linux.cc

@@ -5,8 +5,6 @@
 #include <dlfcn.h>
 #include <fcntl.h>
 #include <stdint.h>
-#include <sys/prctl.h>
-
 #include <memory>
 
 #include "base/android/library_loader/anchor_functions.h"
@@ -230,44 +228,6 @@ uint32_t ReadLinuxProcSmapsFile(FILE* smaps_file,
   return num_valid_regions;
 }
 
-// RAII class making the current process dumpable via prctl(PR_SET_DUMPABLE, 1),
-// in case it is not currently dumpable as described in proc(5) and prctl(2).
-// Noop if the original dumpable state could not be determined.
-class ScopedProcessSetDumpable {
- public:
-  ScopedProcessSetDumpable() {
-    int result = prctl(PR_GET_DUMPABLE, 0, 0, 0, 0);
-    if (result < 0) {
-      PLOG(ERROR) << "prctl";
-      AvoidPrctlOnDestruction();
-      return;
-    }
-    was_dumpable_ = result > 0;
-
-    if (!was_dumpable_) {
-      if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) != 0) {
-        PLOG(ERROR) << "prctl";
-        // PR_SET_DUMPABLE is often disallowed, avoid crashing in this case.
-        AvoidPrctlOnDestruction();
-      }
-    }
-  }
-
-  ScopedProcessSetDumpable(const ScopedProcessSetDumpable&) = delete;
-  ScopedProcessSetDumpable& operator=(const ScopedProcessSetDumpable&) = delete;
-
-  ~ScopedProcessSetDumpable() {
-    if (!was_dumpable_) {
-      PCHECK(prctl(PR_SET_DUMPABLE, 0, 0, 0, 0));
-    }
-  }
-
- private:
-  void AvoidPrctlOnDestruction() { was_dumpable_ = true; }
-
-  bool was_dumpable_;
-};
-
 }  // namespace
 
 FILE* g_proc_smaps_for_testing = nullptr;
@@ -368,14 +328,8 @@ OSMetrics::MappedAndResidentPagesDumpState OSMetrics::GetMappedAndResidentPages(
 
   base::ScopedFILE pagemap_file(fopen(kPagemap, "r"));
   if (!pagemap_file.get()) {
-    {
-      ScopedProcessSetDumpable set_dumpable;
-      pagemap_file.reset(fopen(kPagemap, "r"));
-    }
-    if (!pagemap_file.get()) {
-      DLOG(WARNING) << "Could not open " << kPagemap;
-      return OSMetrics::MappedAndResidentPagesDumpState::kAccessPagemapDenied;
-    }
+    DLOG(WARNING) << "Could not open " << kPagemap;
+    return OSMetrics::MappedAndResidentPagesDumpState::kAccessPagemapDenied;
   }
 
   const size_t kPageSize = base::GetPageSize();