Add tokens for highp/mediump/lowp.

At present, they aren't hooked up to anything. They will be made
functional in followup CLs.

Change-Id: I4bfc25eb4e19fce4c36ea0b55494bf37b2a9ee23
Bug: skia:12248
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/430637
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

gn/sksl_tests.gni

@@ -343,6 +343,7 @@ sksl_shared_tests = [
   "/sksl/shared/OutParamsNoInline.sksl",
   "/sksl/shared/OutParamsTricky.sksl",
   "/sksl/shared/Overflow.sksl",
+  "/sksl/shared/PrecisionQualifiers.sksl",
   "/sksl/shared/RectangleTexture.sksl",
   "/sksl/shared/ResizeMatrix.sksl",
   "/sksl/shared/ResizeMatrixNonsquare.sksl",

resources/sksl/shared/PrecisionQualifiers.sksl

@@ -0,0 +1,9 @@
+uniform half4 colorGreen;
+
+half4 main(float2 coords) {
+    highp vec4 zero = 0;
+    mediump vec4 green = colorGreen;
+    lowp vec4 one = 1;
+
+    return green * one + zero;
+}

src/sksl/SkSLLexer.h

@@ -47,6 +47,9 @@ struct Token {
         TK_HASSIDEEFFECTS,
         TK_STRUCT,
         TK_LAYOUT,
+        TK_HIGHP,
+        TK_MEDIUMP,
+        TK_LOWP,
         TK_IDENTIFIER,
         TK_DIRECTIVE,
         TK_LPAREN,

src/sksl/generated/sksl_public.dehydrated.sksl

@@ -1327,7 +1327,7 @@ static uint8_t SKSL_INCLUDE_sksl_public[] = {4,2,
 45,139,1,2,
 1,
 44,
-54,138,1,0,3,0,1,2,46,
+54,138,1,0,3,0,1,2,49,
 26,
 45,123,0,155,0,2,
 44,
@@ -1344,7 +1344,7 @@ static uint8_t SKSL_INCLUDE_sksl_public[] = {4,2,
 45,142,1,2,
 1,
 44,
-54,141,1,0,3,0,1,2,46,
+54,141,1,0,3,0,1,2,49,
 26,
 45,115,0,147,0,2,
 44,

src/sksl/lex/sksl.lex

@@ -39,6 +39,9 @@ NOINLINE       = "noinline"
 HASSIDEEFFECTS = "sk_has_side_effects"
 STRUCT         = "struct"
 LAYOUT         = "layout"
+HIGHP          = "highp"
+MEDIUMP        = "mediump"
+LOWP           = "lowp"
 IDENTIFIER     = [a-zA-Z_$]([0-9]|[a-zA-Z_$])*
 DIRECTIVE      = #[a-zA-Z_$]([0-9]|[a-zA-Z_$])*
 LPAREN         = "("

tests/sksl/shared/PrecisionQualifiers.asm.frag

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 4: expected expression, but found 'highp'
+1 error

tests/sksl/shared/PrecisionQualifiers.glsl

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 4: expected expression, but found 'highp'
+1 error

tests/sksl/shared/PrecisionQualifiers.metal

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 4: expected expression, but found 'highp'
+1 error