Add reset function to CanvasRenderingContext2D

This functionresets everything (transformation stack, clip, styles,
font, etc). If there are pending transforms in the stack they get
discarded as well.

In the interest of getting the API ready for demoing I'm rushing
through these a bit.

TODO: Add WPT tests (crbug.com/1131449)

Bug: 1131137
Change-Id: If98217fe4de804352d279aa46ab128e3bf6ae53d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425067Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Yi Xu <yiyix@chromium.org>
Reviewed-by: Juanmi Huertas <juanmihd@chromium.org>
Commit-Queue: Aaron Krajeski <aaronhk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812128}

third_party/blink/renderer/modules/canvas/canvas2d/base_rendering_context_2d.cc

@@ -138,7 +138,7 @@ void BaseRenderingContext2D::UnwindStateStack() {
   }
 }
 
-void BaseRenderingContext2D::Reset() {
+void BaseRenderingContext2D::reset() {
   ValidateStateStack();
   UnwindStateStack();
   state_stack_.resize(1);

third_party/blink/renderer/modules/canvas/canvas2d/base_rendering_context_2d.h

@@ -32,8 +32,6 @@ class MODULES_EXPORT BaseRenderingContext2D : public GarbageCollectedMixin,
  public:
   ~BaseRenderingContext2D() override;
 
-  void Reset();
-
   void strokeStyle(StringOrCanvasGradientOrCanvasPattern&) const;
   void setStrokeStyle(const StringOrCanvasGradientOrCanvasPattern&);
 
@@ -81,6 +79,7 @@ class MODULES_EXPORT BaseRenderingContext2D : public GarbageCollectedMixin,
 
   void save();
   void restore();
+  void reset();
 
   void scale(double sx, double sy);
   void rotate(double angle_in_radians);

third_party/blink/renderer/modules/canvas/canvas2d/canvas_rendering_context_2d.cc

@@ -321,7 +321,7 @@ CanvasPixelFormat CanvasRenderingContext2D::PixelFormat() const {
 
 void CanvasRenderingContext2D::Reset() {
   // This is a multiple inheritance bootstrap
-  BaseRenderingContext2D::Reset();
+  BaseRenderingContext2D::reset();
 }
 
 void CanvasRenderingContext2D::RestoreCanvasMatrixClipStack(

third_party/blink/renderer/modules/canvas/canvas2d/canvas_rendering_context_2d.idl

@@ -52,6 +52,8 @@ interface CanvasRenderingContext2D {
     // state
     void save(); // push state on state stack
     void restore(); // pop state stack and restore state
+    // Clear the canvas and reset the path
+    [RuntimeEnabled=NewCanvas2DAPI] void reset();
 
     // transformations (default transform is the identity matrix)
     void scale(unrestricted double x, unrestricted double y);
@@ -157,7 +159,6 @@ interface CanvasRenderingContext2D {
     attribute DOMString textAlign; // "start", "end", "left", "right", "center" (default: "start")
     attribute DOMString textBaseline; // "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" (default: "alphabetic")
     attribute DOMString direction; // "inherit", "rtl", "ltr" (default: "inherit")
-
 };
 
 CanvasRenderingContext2D includes CanvasPath;

third_party/blink/renderer/modules/canvas/offscreencanvas2d/offscreen_canvas_rendering_context_2d.cc

@@ -177,7 +177,7 @@ OffscreenCanvasRenderingContext2D::GetCanvasResourceProvider() const {
 }
 void OffscreenCanvasRenderingContext2D::Reset() {
   Host()->DiscardResourceProvider();
-  BaseRenderingContext2D::Reset();
+  BaseRenderingContext2D::reset();
   // Because the host may have changed to a zero size
   is_valid_size_ = IsValidImageSize(Host()->Size());
 }

third_party/blink/renderer/modules/canvas/offscreencanvas2d/offscreen_canvas_rendering_context_2d.idl

@@ -16,6 +16,8 @@
     // state
     void save(); // push state on state stack
     void restore(); // pop state stack and restore state
+    // Clear the canvas and reset the path
+    [RuntimeEnabled=NewCanvas2DAPI] void reset();
 
     // transformations (default transform is the identity matrix)
     void scale(unrestricted double x, unrestricted double y);

third_party/blink/web_tests/http/tests/serviceworker/webexposed/global-interface-listing-service-worker-expected.txt

@@ -1065,6 +1065,7 @@ interface OffscreenCanvasRenderingContext2D
     method putImageData
     method quadraticCurveTo
     method rect
+    method reset
     method resetTransform
     method restore
     method rotate

third_party/blink/web_tests/webexposed/global-interface-listing-dedicated-worker-expected.txt

@@ -1031,6 +1031,7 @@ Starting worker: resources/global-interface-listing-worker.js
 [Worker]     method putImageData
 [Worker]     method quadraticCurveTo
 [Worker]     method rect
+[Worker]     method reset
 [Worker]     method resetTransform
 [Worker]     method restore
 [Worker]     method rotate

third_party/blink/web_tests/webexposed/global-interface-listing-expected.txt

@@ -1022,6 +1022,7 @@ interface CanvasRenderingContext2D
     method quadraticCurveTo
     method rect
     method removeHitRegion
+    method reset
     method resetTransform
     method restore
     method rotate
@@ -5744,6 +5745,7 @@ interface OffscreenCanvasRenderingContext2D
     method putImageData
     method quadraticCurveTo
     method rect
+    method reset
     method resetTransform
     method restore
     method rotate

third_party/blink/web_tests/webexposed/global-interface-listing-shared-worker-expected.txt

@@ -985,6 +985,7 @@ Starting worker: resources/global-interface-listing-worker.js
 [Worker]     method putImageData
 [Worker]     method quadraticCurveTo
 [Worker]     method rect
+[Worker]     method reset
 [Worker]     method resetTransform
 [Worker]     method restore
 [Worker]     method rotate