Revert "[Sampling profiler] Restore callee-save registers in V8 unwind"

This reverts commit 440bbbe7.

Reason for revert: causing crashes seen in https://crbug.com/1144621

Original change's description:
> [Sampling profiler] Restore callee-save registers in V8 unwind
>
> Restore the callee-save registers now provided in the V8 API when
> unwinding. This is a necessary condition to support unwinds of
> functions that use dynamic stack allocation, which is failure mode
> 1 in the corresponding bug.
>
> Bug: 1122124
> Change-Id: Ifb30bbdd9df343251a7c215e5a5fc140754ac216
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500453
> Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
> Commit-Queue: Mike Wittman <wittman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#822204}

TBR=wittman@chromium.org,etiennep@chromium.org

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

Bug: 1122124, 1144621
Change-Id: I0e998ab210537a513cfc9a67d5e632b2aa73d9ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2515202Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Mike Wittman <wittman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823393}

chrome/renderer/v8_unwinder.cc

@@ -8,14 +8,6 @@
 #include <memory>
 #include <utility>
 
-#include "build/build_config.h"
-
-#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
-// V8 requires the embedder to establish the architecture define.
-#define V8_TARGET_ARCH_ARM 1
-#include "v8/include/v8-unwinder-state.h"
-#endif
-
 namespace {
 
 class V8Module : public base::ModuleCache::Module {
@@ -84,52 +76,6 @@ v8::MemoryRange GetEmbeddedCodeRange(v8::Isolate* isolate) {
   return range;
 }
 
-void CopyCalleeSavedRegisterFromRegisterContext(
-    const base::RegisterContext& register_context,
-    v8::CalleeSavedRegisters* callee_saved_registers) {
-#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
-  // ARM requires callee-saved registers to be restored:
-  // https://crbug.com/v8/10799.
-  DCHECK(callee_saved_registers);
-  callee_saved_registers->arm_r4 =
-      reinterpret_cast<void*>(register_context.arm_r4);
-  callee_saved_registers->arm_r5 =
-      reinterpret_cast<void*>(register_context.arm_r5);
-  callee_saved_registers->arm_r6 =
-      reinterpret_cast<void*>(register_context.arm_r6);
-  callee_saved_registers->arm_r7 =
-      reinterpret_cast<void*>(register_context.arm_r7);
-  callee_saved_registers->arm_r8 =
-      reinterpret_cast<void*>(register_context.arm_r8);
-  callee_saved_registers->arm_r9 =
-      reinterpret_cast<void*>(register_context.arm_r9);
-  callee_saved_registers->arm_r10 =
-      reinterpret_cast<void*>(register_context.arm_r10);
-#endif
-}
-
-void CopyCalleeSavedRegisterToRegisterContext(
-    const v8::CalleeSavedRegisters* callee_saved_registers,
-    base::RegisterContext& register_context) {
-#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
-  DCHECK(callee_saved_registers);
-  register_context.arm_r4 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r4);
-  register_context.arm_r5 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r5);
-  register_context.arm_r6 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r6);
-  register_context.arm_r7 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r7);
-  register_context.arm_r8 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r8);
-  register_context.arm_r9 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r9);
-  register_context.arm_r10 =
-      reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r10);
-#endif
-}
-
 }  // namespace
 
 V8Unwinder::V8Unwinder(v8::Isolate* isolate)
@@ -253,9 +199,6 @@ base::UnwindResult V8Unwinder::TryUnwind(
   register_state.fp = reinterpret_cast<void*>(
       base::RegisterContextFramePointer(thread_context));
 
-  CopyCalleeSavedRegisterFromRegisterContext(*thread_context,
-                                             register_state.callee_saved.get());
-
   if (!v8::Unwinder::TryUnwindV8Frames(
           js_entry_stubs_, code_ranges_.size(), code_ranges_.buffer(),
           &register_state, reinterpret_cast<const void*>(stack_top))) {
@@ -274,9 +217,6 @@ base::UnwindResult V8Unwinder::TryUnwind(
   base::RegisterContextFramePointer(thread_context) =
       reinterpret_cast<uintptr_t>(register_state.fp);
 
-  CopyCalleeSavedRegisterToRegisterContext(register_state.callee_saved.get(),
-                                           *thread_context);
-
   stack->emplace_back(
       base::RegisterContextInstructionPointer(thread_context),
       module_cache->GetModuleForAddress(