[ package:vm_service ] Update changelog for 7.2.0 release

TEST=N/A
TBR=rmacnak@google.com

Change-Id: I1b4f4e937895f4772a01f7d4d75d89d1850cf6e5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/208301
Reviewed-by: Ben Konyi <bkonyi@google.com>

Author: bkonyi

pkg/vm_service/CHANGELOG.md

@@ -1,8 +1,11 @@
 # Changelog
 
 ## 7.2.0
-- Update to version `3.49` of the spec.
+- Update to version `3.50` of the spec.
 - Added `CpuSamples` event kind, and `cpuSamples` property to `Event`.
+- Added `returnType`, `parameters`, and `typeParameters` to `InstanceRef`,
+  and `implicit` to `FunctionRef`.
+- Added `Parameter` type.
 
 ## 7.1.1
 - Update to version `3.48` of the spec.