Add Function based profile tree

runtime/vm/instructions_arm64.cc

Index: runtime/vm/instructions_arm64.cc
diff --git a/runtime/vm/instructions_arm64.cc b/runtime/vm/instructions_arm64.cc
index de513c7b6534e3bfd7aabb83d418317efd7eae9d..aea111fdc4d1e78a07a5d48ed21466b6c1d2139c 100644
--- a/runtime/vm/instructions_arm64.cc
+++ b/runtime/vm/instructions_arm64.cc
@@ -365,6 +365,19 @@ void JumpPattern::SetTargetAddress(uword target_address) const {
   CPU::FlushICache(pc_, 4 * Instr::kInstrSize);
 }
 
+
+ReturnPattern::ReturnPattern(uword pc)
+    : pc_(pc) {
+}
+
+
+bool ReturnPattern::IsValid() const {
+  Instr* bx_lr = Instr::At(pc_);
+  const Register crn = ConcreteRegister(LR);
+  const int32_t instruction = RET | (static_cast<int32_t>(crn) << kRnShift);
+  return bx_lr->InstructionBits() == instruction;
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64