Fix Dart_GlobalTimelineGetTrace to null terminate the string

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index 501091ce9309106c86b0412ee7e485659311fed9..b11ffb418aa2848a95ddd4cb5e1bf39eadcd42e7 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -9562,6 +9562,12 @@ TEST_CASE(Timeline_Dart_TimelineGetTrace) {
   EXPECT(buffer_length > 0);
   EXPECT(buffer != NULL);
 
+  // Response starts with a '{' character and not a '['.
+  EXPECT(buffer[0] == '{');
+  // Response ends with a '}' character and not a ']'.
+  EXPECT(buffer[buffer_length - 1] == '\0');
+  EXPECT(buffer[buffer_length - 2] == '}');
+
   // Heartbeat test.
   EXPECT_SUBSTRING("\"cat\":\"Compiler\"", buffer);
   EXPECT_SUBSTRING("\"name\":\"CompileFunction\"", buffer);
@@ -9609,6 +9615,12 @@ TEST_CASE(Timeline_Dart_TimelineGetTraceOnlyDartEvents) {
   EXPECT(buffer_length > 0);
   EXPECT(buffer != NULL);
 
+  // Response starts with a '{' character and not a '['.
+  EXPECT(buffer[0] == '{');
+  // Response ends with a '}' character and not a ']'.
+  EXPECT(buffer[buffer_length - 1] == '\0');
+  EXPECT(buffer[buffer_length - 2] == '}');
+
   // Heartbeat test.
   EXPECT_SUBSTRING("\"cat\":\"Dart\"", buffer);
   EXPECT_SUBSTRING("\"name\":\"DART_NAME\"", buffer);
@@ -9654,6 +9666,12 @@ TEST_CASE(Timeline_Dart_TimelineGetTraceWithDartEvents) {
   EXPECT(buffer_length > 0);
   EXPECT(buffer != NULL);
 
+  // Response starts with a '{' character and not a '['.
+  EXPECT(buffer[0] == '{');
+  // Response ends with a '}' character and not a ']'.
+  EXPECT(buffer[buffer_length - 1] == '\0');
+  EXPECT(buffer[buffer_length - 2] == '}');
+
   // Heartbeat test.
   EXPECT_SUBSTRING("\"cat\":\"Compiler\"", buffer);
   EXPECT_SUBSTRING("\"name\":\"CompileFunction\"", buffer);
@@ -9697,6 +9715,12 @@ TEST_CASE(Timeline_Dart_TimelineGetTraceGlobalOverride) {
   EXPECT(buffer_length > 0);
   EXPECT(buffer != NULL);
 
+  // Response starts with a '{' character and not a '['.
+  EXPECT(buffer[0] == '{');
+  // Response ends with a '}' character and not a ']'.
+  EXPECT(buffer[buffer_length - 1] == '\0');
+  EXPECT(buffer[buffer_length - 2] == '}');
+
   // Heartbeat test.
   EXPECT_SUBSTRING("\"cat\":\"Compiler\"", buffer);
   EXPECT_SUBSTRING("\"name\":\"CompileFunction\"", buffer);
@@ -9745,6 +9769,12 @@ TEST_CASE(Timeline_Dart_GlobalTimelineGetTrace) {
   EXPECT(buffer_length > 0);
   EXPECT(buffer != NULL);
 
+  // Response starts with a '{' character and not a '['.
+  EXPECT(buffer[0] == '{');
+  // Response ends with a '}' character and not a ']'.
+  EXPECT(buffer[buffer_length - 1] == '\0');
+  EXPECT(buffer[buffer_length - 2] == '}');
+
   // Heartbeat test.
   EXPECT_SUBSTRING("\"name\":\"TestVMDuration\"", buffer);
   EXPECT_SUBSTRING("\"cat\":\"Compiler\"", buffer);
@@ -9779,6 +9809,11 @@ TEST_CASE(Timeline_Dart_GlobalTimelineGetTrace) {
   buffer_length = data.buffer_length;
   EXPECT(buffer_length > 0);
   EXPECT(buffer != NULL);
+  // Response starts with a '{' character and not a '['.
+  EXPECT(buffer[0] == '{');
+  // Response ends with a '}' character and not a ']'.
+  EXPECT(buffer[buffer_length - 1] == '\0');
+  EXPECT(buffer[buffer_length - 2] == '}');
 
   // Heartbeat test for old events.
   EXPECT_SUBSTRING("\"name\":\"TestVMDuration\"", buffer);