fixed premultiplied colors for antialiased colors (#165839)

Previously line.frag was serving up unpremultiplied colors. This
resulted in weird blending and the antialiasing not showing up in most
cases.

test: existing golden will change

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engine/src/flutter/impeller/entity/contents/line_contents.cc

@@ -162,7 +162,7 @@ bool LineContents::Render(const ContentContext& renderer,
 
   VS::FrameInfo frame_info;
   FS::FragInfo frag_info;
-  frag_info.color = color_.Premultiply();
+  frag_info.color = color_;
 
   PipelineBuilderCallback pipeline_callback =
       [&renderer](ContentContextOptions options) {

engine/src/flutter/impeller/entity/shaders/line.frag

@@ -4,6 +4,7 @@
 
 precision mediump float;
 
+#include <impeller/color.glsl>
 #include <impeller/types.glsl>
 
 uniform FragInfo {
@@ -41,4 +42,5 @@ float CalculateLine() {
 void main() {
   float line = CalculateLine();
   frag_color = vec4(frag_info.color.xyz, line);
+  frag_color = IPPremultiply(frag_color);
 }

engine/src/flutter/impeller/tools/malioc.json

@@ -4431,16 +4431,16 @@
       "uses_late_zs_update": false,
       "variants": {
         "Main": {
-          "fp16_arithmetic": 6,
+          "fp16_arithmetic": 0,
           "has_stack_spilling": false,
           "performance": {
             "longest_path_bound_pipelines": [
               "varying"
             ],
             "longest_path_cycles": [
-              0.21875,
-              0.140625,
-              0.21875,
+              0.1875,
+              0.1875,
+              0.1875,
               0.0,
               0.0,
               1.75,
@@ -4459,9 +4459,9 @@
               "varying"
             ],
             "shortest_path_cycles": [
-              0.140625,
-              0.125,
-              0.140625,
+              0.171875,
+              0.171875,
+              0.109375,
               0.0,
               0.0,
               1.75,
@@ -4471,9 +4471,9 @@
               "varying"
             ],
             "total_cycles": [
-              0.21875,
-              0.140625,
-              0.21875,
+              0.1875,
+              0.1875,
+              0.1875,
               0.0,
               0.0,
               1.75,
@@ -8251,7 +8251,7 @@
       "uses_late_zs_update": false,
       "variants": {
         "Main": {
-          "fp16_arithmetic": 15,
+          "fp16_arithmetic": 33,
           "has_stack_spilling": false,
           "performance": {
             "longest_path_bound_pipelines": [
@@ -8259,8 +8259,8 @@
             ],
             "longest_path_cycles": [
               0.1875,
-              0.140625,
-              0.1875,
+              0.171875,
+              0.15625,
               0.1875,
               0.0,
               1.75,
@@ -8280,8 +8280,8 @@
             ],
             "shortest_path_cycles": [
               0.1875,
-              0.125,
-              0.140625,
+              0.15625,
+              0.109375,
               0.1875,
               0.0,
               1.75,
@@ -8292,8 +8292,8 @@
             ],
             "total_cycles": [
               0.1875,
-              0.140625,
-              0.1875,
+              0.171875,
+              0.15625,
               0.1875,
               0.0,
               1.75,
@@ -8302,7 +8302,7 @@
           },
           "stack_spill_bytes": 0,
           "thread_occupancy": 100,
-          "uniform_registers_used": 6,
+          "uniform_registers_used": 4,
           "work_registers_used": 18
         }
       }