perf: Revert "perf: remove unnecessary context.save()& `context.res…

…tore()`"

This reverts commit f7b488e.

For some reason in Chromium 95.0.4638.54 (and maybe others) that change
caused `render()` CPU time to grow over time. For me on the
`examples/example1.html` page it would grow from 0.5ms to 50ms over 5 minutes

smoothie.js

@@ -859,6 +859,10 @@
 
     context.font = chartOptions.labels.fontSize + 'px ' + chartOptions.labels.fontFamily;
 
+    // Save the state of the canvas context, any transformations applied in this method
+    // will get removed from the stack at the end of this method when .restore() is called.
+    context.save();
+
     // Move the origin.
     context.translate(dimensions.left, dimensions.top);
 
@@ -870,11 +874,14 @@
     context.clip();
 
     // Clear the working area.
+    context.save();
     context.fillStyle = chartOptions.grid.fillStyle;
     context.clearRect(0, 0, dimensions.width, dimensions.height);
     context.fillRect(0, 0, dimensions.width, dimensions.height);
+    context.restore();
 
     // Grid lines...
+    context.save();
     context.lineWidth = chartOptions.grid.lineWidth;
     context.strokeStyle = chartOptions.grid.strokeStyle;
     // Vertical (time) dividers.
@@ -912,6 +919,7 @@
       context.strokeRect(0, 0, dimensions.width, dimensions.height);
       context.closePath();
     }
+    context.restore();
 
     // Draw any horizontal lines...
     if (chartOptions.horizontalLines && chartOptions.horizontalLines.length) {
@@ -938,6 +946,7 @@
       if (dataSet.length <= 1 || timeSeries.disabled) {
           continue;
       }
+      context.save();
 
       var seriesOptions = this.seriesSet[d].options;
 
@@ -1019,6 +1028,8 @@
         context.strokeStyle = seriesOptions.strokeStyle;
         context.stroke();
       }
+
+      context.restore();
     }
 
     if (chartOptions.tooltip && this.mouseX >= 0) {
@@ -1116,6 +1127,8 @@
       context.fillStyle = chartOptions.title.fillStyle;
       context.fillText(chartOptions.title.text, titleXPos, titleYPos);
     }
+
+    context.restore(); // See .save() above.
   };
 
   // Sample timestamp formatting function