DevTools: initial support of box selection on FlameChart

Source/devtools/front_end/components/flameChart.css

Index: Source/devtools/front_end/components/flameChart.css
diff --git a/Source/devtools/front_end/components/flameChart.css b/Source/devtools/front_end/components/flameChart.css
index c27f53051f88b587708fd5b042af5183f10000e4..b583dff3853191db90049de593f2dbc088ce4cee 100644
--- a/Source/devtools/front_end/components/flameChart.css
+++ b/Source/devtools/front_end/components/flameChart.css
@@ -40,3 +40,17 @@ body.platform-mac .flame-chart-v-scroll {
     right: 0;
     bottom: 0;
 }
+
+.flame-chart-selection-overlay {
+    position: absolute;
+    z-index: 100;
+    background-color: rgba(56, 121, 217, 0.3);
+    border-color: rgb(16, 81, 177);
+    border-width: 1px;
+    border-style: solid;
+    pointer-events:none;
+}
+
+.flame-chart-selection-overlay .time-span {
+    white-space: nowrap;
+}