cmd/trace: document that trace viewer is only tested on chromium

Fixes #19207

Change-Id: I69b70492fd01599a13c1a3beb87f492de40a18b0
Reviewed-on: https://go-review.googlesource.com/37312Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/trace/doc.go

@@ -26,5 +26,10 @@ Supported profile types are:
 
 Then, you can use the pprof tool to analyze the profile:
 	go tool pprof TYPE.pprof
+
+Note that while the various profiles available when launching
+'go tool trace' work on every browser, the trace viewer itself
+(the 'view trace' page) comes from the Chrome/Chromium project
+and is only actively tested on that browser.
 */
 package main

src/cmd/trace/main.go

@@ -42,6 +42,11 @@ Supported profile types are:
 Flags:
 	-http=addr: HTTP service address (e.g., ':6060')
 	-pprof=type: print a pprof-like profile instead
+
+Note that while the various profiles available when launching
+'go tool trace' work on every browser, the trace viewer itself
+(the 'view trace' page) comes from the Chrome/Chromium project
+and is only actively tested on that browser.
 `
 
 var (