Reland "Reland "Remove GrProgramDesc::KeyHeader structure""

This is a reland of 202420e0147b02f963de761a903b2c430dfa0cec

Original change's description:
> Reland "Remove GrProgramDesc::KeyHeader structure"
>
> This is a reland of 4bcd58afbf1a1993e453231c575b47a0ae1ec24d
>
> Original change's description:
> > Remove GrProgramDesc::KeyHeader structure
> >
> > Instead, just fold all of this information into the key, like everything
> > else. The only value that was accessed elsewhere is the initial key
> > length. That doesn't need to be part of the key, so store it separately
> > in the GrProgramDesc.
> >
> > Removing this special case logic is just the first step in revising how
> > we assemble keys.
> >
> > Bug: skia:11372
> > Change-Id: I52eb76812045e1906797cb37e809cfd0b3332ef0
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376797
> > Reviewed-by: Brian Salomon <bsalomon@google.com>
> > Commit-Queue: Brian Osman <brianosman@google.com>
>
> Bug: skia:11372
> Change-Id: I2cdb49aee3537e54dad9af1f9b47cf1aed1aca21
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376849
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

Cq-Include-Trybots: luci.skia.skia.primary:Build-Win-MSVC-x86-Debug
Bug: skia:11372
Change-Id: I7cc94015d93fcb0365b6aa35daa1f9ea2facdd16
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377836
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/GrProgramDesc.cpp b/src/gpu/GrProgramDesc.cpp
index c8b266f..e11d06a 100644
--- a/src/gpu/GrProgramDesc.cpp
+++ b/src/gpu/GrProgramDesc.cpp
@@ -175,11 +175,7 @@
     // bindings in use or other descriptor field settings) it should be set
     // to a canonical value to avoid duplicate programs with different keys.
 
-    static_assert(0 == kProcessorKeysOffset % sizeof(uint32_t));
-    // Make room for everything up to the effect keys.
     desc->key().reset();
-    desc->key().push_back_n(kProcessorKeysOffset);
-
     GrProcessorKeyBuilder b(&desc->key());
 
     const GrPrimitiveProcessor& primitiveProcessor = programInfo.primProc();
@@ -223,36 +219,29 @@
         b.add32(renderTarget->getSamplePatternKey());
     }
 
-    // --------DO NOT MOVE HEADER ABOVE THIS LINE--------------------------------------------------
-    // Because header is a pointer into the dynamic array, we can't push any new data into the key
-    // below here.
-    KeyHeader* header = desc->atOffset<KeyHeader, kHeaderOffset>();
-
-    // make sure any padding in the header is zeroed.
-    memset(header, 0, kHeaderSize);
-    header->fWriteSwizzle = pipeline.writeSwizzle().asKey();
-    header->fColorFragmentProcessorCnt = numColorFPs;
-    header->fCoverageFragmentProcessorCnt = numCoverageFPs;
-    SkASSERT(header->fColorFragmentProcessorCnt == numColorFPs);
-    SkASSERT(header->fCoverageFragmentProcessorCnt == numCoverageFPs);
+    // Add "header" metadata
+    uint32_t header = 0;
+    SkDEBUGCODE(uint32_t header_bits = 0);
+    auto add_bits = [&](uint32_t nbits, uint32_t val) {
+        SkASSERT(val < (1u << nbits));
+        SkASSERT((header_bits += nbits) <= 32);
+        header = (header << nbits) | val;
+    };
+    add_bits(16, pipeline.writeSwizzle().asKey());
+    add_bits( 1, numColorFPs);
+    add_bits( 2, numCoverageFPs);
     // If we knew the shader won't depend on origin, we could skip this (and use the same program
     // for both origins). Instrumenting all fragment processors would be difficult and error prone.
-    header->fSurfaceOriginKey =
-                    GrGLSLFragmentShaderBuilder::KeyForSurfaceOrigin(programInfo.origin());
-    header->fProcessorFeatures = (uint8_t)programInfo.requestedFeatures();
-    // Ensure enough bits.
-    SkASSERT(header->fProcessorFeatures == (int) programInfo.requestedFeatures());
-    header->fSnapVerticesToPixelCenters = pipeline.snapVerticesToPixelCenters();
+    add_bits( 2, GrGLSLFragmentShaderBuilder::KeyForSurfaceOrigin(programInfo.origin()));
+    add_bits( 1, static_cast<uint32_t>(programInfo.requestedFeatures()));
+    add_bits( 1, pipeline.snapVerticesToPixelCenters());
     // The base descriptor only stores whether or not the primitiveType is kPoints. Backend-
     // specific versions (e.g., Vulkan) require more detail
-    header->fHasPointSize = (programInfo.primitiveType() == GrPrimitiveType::kPoints);
+    add_bits( 1, (programInfo.primitiveType() == GrPrimitiveType::kPoints));
 
-    header->fInitialKeyLength = desc->keyLength();
-    // Fail if the initial key length won't fit in 27 bits.
-    if (header->fInitialKeyLength != desc->keyLength()) {
-        desc->key().reset();
-        return false;
-    }
+    b.add32(header);
+
+    desc->fInitialKeyLength = desc->keyLength();
 
     return true;
 }