Bug 1224201 - mem. profiler : reduce font-size & add column min-width (16ch);r=vporof

Goal of this commit is to ensure we can display at least 12 number digits +
4 percent chars in the memory table columns whatever the viewport size.
With a viewport width of 800px, we still have 200px usable for the last col
in census view

Some items of the memory table are already using 90% font size.
This commit applies this font-size to the whole memory table.
Also added a 16ch min-width to the non-flex columns

devtools/client/themes/memory.css

@@ -233,6 +233,7 @@ html, body, #app, #memory-tool {
    * (https://drafts.csswg.org/css-flexbox/#min-size-auto)
    */
   min-width: 0;
+  font-size: 90%;
 }
 
 #heap-view > .heap-view-panel {
@@ -294,7 +295,6 @@ html, body, #app, #memory-tool {
   text-overflow: ellipsis;
   line-height: var(--heap-tree-header-height);
   justify-content: center;
-  font-size: 90%;
   white-space: nowrap;
 }
 
@@ -317,6 +317,7 @@ html, body, #app, #memory-tool {
 
 .tree-node {
   height: var(--heap-tree-row-height);
+  line-height: var(--heap-tree-row-height);
 }
 
 /**
@@ -363,6 +364,12 @@ html, body, #app, #memory-tool {
 .heap-tree-item-bytes,
 .heap-tree-item-total-bytes {
   width: 10%;
+  /*
+   * Provision for up to :
+   * - 12 characters for the number part (10s of GB and spaces every 3 digits)
+   * - 4 chars for the percent part (the maximum length string is "100%")
+   */
+  min-width: 16ch;
 }
 
 .heap-tree-item-name {
@@ -410,7 +417,7 @@ html, body, #app, #memory-tool {
 }
 
 .heap-tree-percent {
-  width: 2.5em;
+  width: 4ch;
 }
 
 .heap-tree-item.focused .heap-tree-number,
@@ -487,9 +494,9 @@ html, body, #app, #memory-tool {
 }
 
 .no-allocation-stacks {
-    border-color: var(--theme-splitter-color);
-    border-style: solid;
-    border-width: 0px 0px 1px 0px;
-    text-align: center;
-    padding: 5px;
+  border-color: var(--theme-splitter-color);
+  border-style: solid;
+  border-width: 0px 0px 1px 0px;
+  text-align: center;
+  padding: 5px;
 }