Add HighEntropy annotation to HTMLCanvasElement.getContext() for

identifiability study.

I instrumented this API in http://crrev.com/c/2442138 and accidentally
omitted the HighEntropy IDL annotation.

The annotation adds a use counter to get a broader picture of the API
usage across the web. This supplements the data collected in the
instrumentation which is only recorded for a small fraction of users.

Bug: 973801
Change-Id: I827c56d32d004f6eb42524954cfcad65cadd78dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2472603Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Commit-Queue: Dylan Cutler <dylancutler@google.com>
Cr-Commit-Position: refs/heads/master@{#818481}

third_party/blink/public/mojom/web_feature/web_feature.mojom

@@ -2873,7 +2873,7 @@ enum WebFeature {
   kV8Touch_Force_AttributeGetter = 3542,
   kWebGLRenderingContextMakeXRCompatible = 3543,
   kV8WebGLCompressedTextureASTC_GetSupportedProfiles_Method = 3544,
-  kIdentifiabilityStudyReserved3545 = 3545,
+  kHTMLCanvasGetContext = 3545,
   kV8BeforeInstallPromptEvent_Platforms_AttributeGetter = 3546,
   kIdentifiabilityStudyReserved3547 = 3547,
   kIdentifiabilityStudyReserved3548 = 3548,

third_party/blink/renderer/modules/canvas/htmlcanvas/html_canvas_element_module.idl

@@ -22,7 +22,7 @@ typedef (CanvasRenderingContext2D or
     // requires throwing TypeError if the incoming argument is not an object type
     // (and is not undefined or null). The binding must ignore this.
     // Related spec issue: https://github.com/whatwg/html/issues/595
-    [RaisesException] RenderingContext? getContext(DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributesModule attributes = {});
+    [HighEntropy, MeasureAs=HTMLCanvasGetContext, RaisesException] RenderingContext? getContext(DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributesModule attributes = {});
 
     [CallWith=ExecutionContext, RuntimeEnabled=SurfaceEmbeddingFeatures,
      RaisesException, MeasureAs=OffscreenCanvas] OffscreenCanvas transferControlToOffscreen();

third_party/blink/renderer/modules/canvas/htmlcanvas/html_canvas_element_module_support_webgl2_compute.idl

@@ -23,6 +23,6 @@ typedef (CanvasRenderingContext2D or
     // requires throwing TypeError if the incoming argument is not an object type
     // (and is not undefined or null). The binding must ignore this.
     // Related spec issue: https://github.com/whatwg/html/issues/595
-    [RaisesException] RenderingContext? getContext(DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributesModule attributes = {});
+    [HighEntropy, MeasureAs=HTMLCanvasGetContext, RaisesException] RenderingContext? getContext(DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributesModule attributes = {});
     [CallWith=ExecutionContext, RaisesException, MeasureAs=OffscreenCanvas, RuntimeEnabled=SurfaceEmbeddingFeatures] OffscreenCanvas transferControlToOffscreen();
 };

tools/metrics/histograms/enums.xml

@@ -29777,7 +29777,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3543" label="WebGLRenderingContextMakeXRCompatible"/>
   <int value="3544"
       label="V8WebGLCompressedTextureASTC_GetSupportedProfiles_Method"/>
-  <int value="3545" label="IdentifiabilityStudyReserved3545"/>
+  <int value="3545" label="HTMLCanvasGetContext"/>
   <int value="3546"
       label="V8BeforeInstallPromptEvent_Platforms_AttributeGetter"/>
   <int value="3547" label="IdentifiabilityStudyReserved3547"/>