Replace a lot of 'static const' with 'constexpr' or 'const'.

'static const' means, there must be at most one of these, and initialize it at
compile time if possible or runtime if necessary.  This leads to unexpected
code execution, and TSAN* will complain about races on the guard variables.

Generally 'constexpr' or 'const' are better choices.  Neither can cause races:
they're either intialized at compile time (constexpr) or intialized each time
independently (const).

This CL prefers constexpr where possible, and uses const where not.  It even
prefers constexpr over const where they don't make a difference... I want to have
lots of examples of constexpr for people to see and mimic.

The scoped-to-class static has nothing to do with any of this, and is not changed.

* Not yet on the bots, which use an older TSAN.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2300623005

Review-Url: https://codereview.chromium.org/2300623005
diff --git a/gm/drawbitmaprect.cpp b/gm/drawbitmaprect.cpp
index ea9a09f..3c873e2 100644
--- a/gm/drawbitmaprect.cpp
+++ b/gm/drawbitmaprect.cpp
@@ -131,8 +131,8 @@
 typedef void DrawRectRectProc(SkCanvas*, SkImage*, const SkBitmap&, const SkIRect&, const SkRect&,
                               const SkPaint*);
 
-static const int gSize = 1024;
-static const int gBmpSize = 2048;
+constexpr int gSize = 1024;
+constexpr int gBmpSize = 2048;
 
 class DrawBitmapRectGM : public skiagm::GM {
 public:
@@ -163,10 +163,10 @@
         }
 
         SkRect dstRect = { 0, 0, SkIntToScalar(64), SkIntToScalar(64)};
-        static const int kMaxSrcRectSize = 1 << (SkNextLog2(gBmpSize) + 2);
+        const int kMaxSrcRectSize = 1 << (SkNextLog2(gBmpSize) + 2);
 
-        static const int kPadX = 30;
-        static const int kPadY = 40;
+        const int kPadX = 30;
+        const int kPadY = 40;
         SkPaint paint;
         paint.setAlpha(0x20);
         canvas->drawImageRect(fImage, SkRect::MakeIWH(gSize, gSize), &paint);