Various improvements to stack walking speed

Make BitMemoryRegion constructor inlined, remove read barrier
for IsProxyMethod.

Around 15% speedup for pmd benchmark, maybe more for CC.

Test: test-art-host

Change-Id: Ib4392649e041406e538cc944c26c69f68d388fb4
diff --git a/runtime/bit_memory_region.h b/runtime/bit_memory_region.h
index 90a1981..c3b5be4 100644
--- a/runtime/bit_memory_region.h
+++ b/runtime/bit_memory_region.h
@@ -26,7 +26,7 @@
 class BitMemoryRegion FINAL : public ValueObject {
  public:
   BitMemoryRegion() = default;
-  BitMemoryRegion(MemoryRegion region, size_t bit_offset, size_t bit_size) {
+  ALWAYS_INLINE BitMemoryRegion(MemoryRegion region, size_t bit_offset, size_t bit_size) {
     bit_start_ = bit_offset % kBitsPerByte;
     const size_t start = bit_offset / kBitsPerByte;
     const size_t end = (bit_offset + bit_size + kBitsPerByte - 1) / kBitsPerByte;