trace: Make links in generated HTML be relative to the current path.

This will make it easier to serve /debug/requests off a different path.

This is groundwork towards addressing golang/go#12195.

Change-Id: If29a4c329609df1d5b09a3a88b8bdf1f8b622e49
Reviewed-on: https://go-review.googlesource.com/13824
Reviewed-by: Dave Day <djd@golang.org>

trace/trace.go

@@ -951,7 +951,7 @@ const pageHTML = `
 
 		{{$n := index $.ActiveTraceCount $fam}}
 		<td class="active {{if not $n}}empty{{end}}">
-			{{if $n}}<a href="/debug/requests?fam={{$fam}}&b=-1{{if $.Expanded}}&exp=1{{end}}">{{end}}
+			{{if $n}}<a href="?fam={{$fam}}&b=-1{{if $.Expanded}}&exp=1{{end}}">{{end}}
 			[{{$n}} active]
 			{{if $n}}</a>{{end}}
 		</td>
@@ -960,7 +960,7 @@ const pageHTML = `
 		{{range $i, $b := $f.Buckets}}
 		{{$empty := $b.Empty}}
 		<td {{if $empty}}class="empty"{{end}}>
-		{{if not $empty}}<a href="/debug/requests?fam={{$fam}}&b={{$i}}{{if $.Expanded}}&exp=1{{end}}">{{end}}
+		{{if not $empty}}<a href="?fam={{$fam}}&b={{$i}}{{if $.Expanded}}&exp=1{{end}}">{{end}}
 		[{{.Cond}}]
 		{{if not $empty}}</a>{{end}}
 		</td>
@@ -968,13 +968,13 @@ const pageHTML = `
 
 		{{$nb := len $f.Buckets}}
 		<td class="latency-first">
-		<a href="/debug/requests?fam={{$fam}}&b={{$nb}}">[minute]</a>
+		<a href="?fam={{$fam}}&b={{$nb}}">[minute]</a>
 		</td>
 		<td>
-		<a href="/debug/requests?fam={{$fam}}&b={{add $nb 1}}">[hour]</a>
+		<a href="?fam={{$fam}}&b={{add $nb 1}}">[hour]</a>
 		</td>
 		<td>
-		<a href="/debug/requests?fam={{$fam}}&b={{add $nb 2}}">[total]</a>
+		<a href="?fam={{$fam}}&b={{add $nb 2}}">[total]</a>
 		</td>
 
 	</tr>
@@ -988,25 +988,25 @@ const pageHTML = `
 <h3>Family: {{$.Family}}</h3>
 
 {{if or $.Expanded $.Traced}}
-  <a href="/debug/requests?fam={{$.Family}}&b={{$.Bucket}}">[Normal/Summary]</a>
+  <a href="?fam={{$.Family}}&b={{$.Bucket}}">[Normal/Summary]</a>
 {{else}}
   [Normal/Summary]
 {{end}}
 
 {{if or (not $.Expanded) $.Traced}}
-  <a href="/debug/requests?fam={{$.Family}}&b={{$.Bucket}}&exp=1">[Normal/Expanded]</a>
+  <a href="?fam={{$.Family}}&b={{$.Bucket}}&exp=1">[Normal/Expanded]</a>
 {{else}}
   [Normal/Expanded]
 {{end}}
 
 {{if not $.Active}}
 	{{if or $.Expanded (not $.Traced)}}
-	<a href="/debug/requests?fam={{$.Family}}&b={{$.Bucket}}&rtraced=1">[Traced/Summary]</a>
+	<a href="?fam={{$.Family}}&b={{$.Bucket}}&rtraced=1">[Traced/Summary]</a>
 	{{else}}
 	[Traced/Summary]
 	{{end}}
 	{{if or (not $.Expanded) (not $.Traced)}}
-	<a href="/debug/requests?fam={{$.Family}}&b={{$.Bucket}}&exp=1&rtraced=1">[Traced/Expanded]</a>
+	<a href="?fam={{$.Family}}&b={{$.Bucket}}&exp=1&rtraced=1">[Traced/Expanded]</a>
         {{else}}
 	[Traced/Expanded]
 	{{end}}