DevTools: Rename Document Frames in performance monitor.

Bug: 
Change-Id: I4177e94f6dc7cbb55392f6c70f0c7a711023edf8
Reviewed-on: https://chromium-review.googlesource.com/826364Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524179}

third_party/WebKit/Source/devtools/front_end/timeline/PerformanceMonitor.js

@@ -447,7 +447,7 @@ Timeline.PerformanceMonitor.ControlPane = class extends Common.Object {
       {title: Common.UIString('DOM Nodes'), metrics: [{name: 'Nodes', color: 'green'}]},
       {title: Common.UIString('JS event listeners'), metrics: [{name: 'JSEventListeners', color: 'yellowgreen'}]},
       {title: Common.UIString('Documents'), metrics: [{name: 'Documents', color: 'darkblue'}]},
-      {title: Common.UIString('Frames'), metrics: [{name: 'Frames', color: 'darkcyan'}]},
+      {title: Common.UIString('Document Frames'), metrics: [{name: 'Frames', color: 'darkcyan'}]},
       {title: Common.UIString('Layouts / sec'), metrics: [{name: 'LayoutCount', color: 'hotpink'}]},
       {title: Common.UIString('Style recalcs / sec'), metrics: [{name: 'RecalcStyleCount', color: 'deeppink'}]}
     ];