Add pause/resume for isolates in vmservice/observatory.

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 2f308723dc73c27f69bd7b605721574fe70ce24b..f4ddc35adb66d705372be020d41e1658d776a3b7 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -326,6 +326,19 @@ class Isolate : public BaseIsolate {
     return OFFSET_OF(Isolate, single_step_);
   }
 
+  // Requests that the debugger resume execution.
+  void Resume() {
+    resume_request_ = true;
+  }
+
+  // Returns whether the vm service has requested that the debugger
+  // resume execution.
+  bool GetAndClearResumeRequest() {
+    bool resume_request = resume_request_;
+    resume_request_ = false;
+    return resume_request;
+  }
+
   Random* random() { return &random_; }
 
   Simulator* simulator() const { return simulator_; }
@@ -550,6 +563,7 @@ class Isolate : public BaseIsolate {
   StubCode* stub_code_;
   Debugger* debugger_;
   bool single_step_;
+  bool resume_request_;
   Random random_;
   Simulator* simulator_;
   LongJumpScope* long_jump_base_;