[Code health] Make some members in Blink::PaintWorkletInput const

The Blink::PaintWorkletInput is a const data structure, once it is
created, its member should never be changed.

Bug: 884698
Change-Id: I9ac31481066fb6a6f2f0d02524b4136f3f084d23
Reviewed-on: https://chromium-review.googlesource.com/c/1388108Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618592}

third_party/blink/renderer/core/css/cssom/paint_worklet_input.cc

@@ -17,9 +17,12 @@ PaintWorkletInput::PaintWorkletInput(
     const Vector<AtomicString>& custom_properties)
     : name_(name),
       container_size_(container_size),
-      effective_zoom_(effective_zoom) {
-  style_map_ = MakeGarbageCollected<PaintWorkletStylePropertyMap>(
-      document, style, styled_node, native_properties, custom_properties);
-}
+      effective_zoom_(effective_zoom),
+      style_map_(MakeGarbageCollected<PaintWorkletStylePropertyMap>(
+          document,
+          style,
+          styled_node,
+          native_properties,
+          custom_properties)) {}
 
 }  // namespace blink

third_party/blink/renderer/core/css/cssom/paint_worklet_input.h

@@ -38,12 +38,10 @@ class CORE_EXPORT PaintWorkletInput : public cc::PaintWorkletInput {
   PaintWorkletStylePropertyMap* StyleMap() { return style_map_.Get(); }
 
  private:
-  // TODO(xidachen): these members should be const as they are immutable once
-  // created.
-  std::string name_;
-  FloatSize container_size_;
-  float effective_zoom_;
-  CrossThreadPersistent<PaintWorkletStylePropertyMap> style_map_;
+  const std::string name_;
+  const FloatSize container_size_;
+  const float effective_zoom_;
+  const CrossThreadPersistent<PaintWorkletStylePropertyMap> style_map_;
 };
 
 }  // namespace blink