[blink] Remove no longer used blink::SparseHistogram helper.

All usage has been migrated to use the standard //base/metrics
functions.

Bug: 1047547
Change-Id: I548b683c758f2251a3af1db8280c9c63e6245bd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505932
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Auto-Submit: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821804}

third_party/blink/renderer/platform/instrumentation/histogram.cc

@@ -51,15 +51,6 @@ EnumerationHistogram::EnumerationHistogram(
           boundary_value + 1,
           base::HistogramBase::kUmaTargetedHistogramFlag)) {}
 
-SparseHistogram::SparseHistogram(const char* name) {
-  histogram_ = base::SparseHistogram::FactoryGet(
-      name, base::HistogramBase::kUmaTargetedHistogramFlag);
-}
-
-void SparseHistogram::Sample(base::HistogramBase::Sample sample) {
-  histogram_->Add(sample);
-}
-
 LinearHistogram::LinearHistogram(const char* name,
                                  base::HistogramBase::Sample min,
                                  base::HistogramBase::Sample max,

third_party/blink/renderer/platform/instrumentation/histogram.h

@@ -46,18 +46,6 @@ class PLATFORM_EXPORT EnumerationHistogram : public CustomCountHistogram {
                        base::HistogramBase::Sample boundary_value);
 };
 
-class PLATFORM_EXPORT SparseHistogram {
-  USING_FAST_MALLOC(SparseHistogram);
-
- public:
-  explicit SparseHistogram(const char* name);
-
-  void Sample(base::HistogramBase::Sample);
-
- private:
-  base::HistogramBase* histogram_;
-};
-
 class PLATFORM_EXPORT LinearHistogram : public CustomCountHistogram {
  public:
   explicit LinearHistogram(const char* name,