Cherry-pick 26aaa25. rdar://122309325

    REGRESSION(267824@main): Changing HTMLCanvasElement width, height causes intermediate buffer allocations
    https://bugs.webkit.org/show_bug.cgi?id=268745
    rdar://122309325

    Reviewed by Simon Fraser.

    Resizing is intended to leave the buffer unallocated, so that
    sequential width, height assignments will not allocate multiple times.

    This intention was nullified by CanvasRenderingContext2DBase::reset().
    Calling resetTransform redundantly would recreate the buffer
    immediately from width, height attribute setters.

    The transform reset is redundant, the context transform is reset when
    the context state saver is restored and re-saved.

    Clearing the canvas doesn't need to use public
    CanvasRenderingContext2DBase::clearCanvas() that will mutate the context
    state. The state is in known state with initial transform, and thus it
    doesn't need transform mutation.

    * Source/WebCore/html/canvas/CanvasRenderingContext2DBase.cpp:
    (WebCore::CanvasRenderingContext2DBase::reset):

    Canonical link: https://commits.webkit.org/274135@main

Identifier: 272448.530@safari-7618.1.15.10-branch

LayoutTests/fast/canvas/offscreen-giant-transfer-to-imagebitmap-expected.txt

@@ -1,3 +1,2 @@
 CONSOLE MESSAGE: Canvas area exceeds the maximum limit (width * height > 268435456).
-CONSOLE MESSAGE: Canvas area exceeds the maximum limit (width * height > 268435456).
 

LayoutTests/platform/ios/fast/canvas/offscreen-giant-transfer-to-imagebitmap-expected.txt

@@ -1,3 +1,2 @@
 CONSOLE MESSAGE: Canvas area exceeds the maximum limit (width * height > 16777216).
-CONSOLE MESSAGE: Canvas area exceeds the maximum limit (width * height > 16777216).
 

Source/WebCore/html/canvas/CanvasRenderingContext2DBase.cpp

@@ -272,10 +272,10 @@ void CanvasRenderingContext2DBase::reset()
     m_cachedContents.emplace<CachedContentsTransparent>();
 
     clearAccumulatedDirtyRect();
-    resetTransform();
-
-    canvasBase().resetGraphicsContextState();
-    clearCanvas();
+    if (auto* c = canvasBase().existingDrawingContext()) {
+        canvasBase().resetGraphicsContextState();
+        c->clearRect(FloatRect { { }, canvasBase().size() });
+    }
 }
 
 CanvasRenderingContext2DBase::State::State()