[ddc] Use prototype trick for better chrome performance

After emitting a library, creates a dummy function for each library and
sets the library object as the `.prototype` of the dummy function.

Reverses the performance degradation seen after adding one too many
members to the `dart:_runtime` library in:
https://golem.corp.goog/PerformanceChanges?repository=dart&revision=116131

According to sra@ this serves as a signal to V8 that the members of the
library should get optimized for fast lookup. These golem runs show
performance improvements that support this.

dartdevc performance improvements:
https://golem.corp.goog/Comparison?repository=dart#targetA%3Ddartdevc%3BmachineTypeA%3Dlinux-x64%3BrevisionA%3D116273%3BpatchA%3Dnshahan--ddc--WIP-library-as-prototype-optimization-1%3BtargetB%3Ddartdevc%3BmachineTypeB%3Dlinux-x64%3BrevisionB%3D116238%3BpatchB%3DNone

dartdevc-canary performance improvements:
https://golem.corp.goog/Comparison?repository=dart#targetA%3Ddartdevc-canary%3BmachineTypeA%3Dlinux-x64%3BrevisionA%3D116273%3BpatchA%3Dnshahan--ddc--WIP-library-as-prototype-optimization-1%3BtargetB%3Ddartdevc-canary%3BmachineTypeB%3Dlinux-x64%3BrevisionB%3D116238%3BpatchB%3DNone

Change-Id: Ifee464e393609c30eff4ea7c19da511134eccdcf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427822
Reviewed-by: Nate Biggs <[email protected]>
Commit-Queue: Nicholas Shahan <[email protected]>

Author: nshahan

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -927,6 +927,12 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
       _emitLibraryProcedures(library);
       _emitTopLevelFields(library.fields);
     }
+    // Creating a function and setting the library object as the prototype
+    // serves as a signal to V8 that the members of the library should get
+    // optimized for fast lookup.
+    // Do not remove without testing for performance regressions.
+    _moduleItems.add(js.statement(
+        '(function() {}).prototype = #', [_libraries[_currentLibrary!]]));
     _staticTypeContext.leaveLibrary(_currentLibrary!);
     _currentLibrary = null;
   }

pkg/dev_compiler/lib/src/kernel/compiler_new.dart

@@ -1163,6 +1163,12 @@ class LibraryCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
       library.classes.forEach(_emitClass);
       _emitLibraryMembers(library);
     }
+    // Creating a function and setting the library object as the prototype
+    // serves as a signal to V8 that the members of the library should get
+    // optimized for fast lookup.
+    // Do not remove without testing for performance regressions.
+    _moduleItems.add(js.statement(
+        '(function() {}).prototype = #', [_libraries[_currentLibrary!]]));
     _staticTypeContext.leaveLibrary(_currentLibrary!);
   }